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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..d83eee9 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #67396 (https://www.gutenberg.org/ebooks/67396) diff --git a/old/67396-0.txt b/old/67396-0.txt deleted file mode 100644 index dc2f085..0000000 --- a/old/67396-0.txt +++ /dev/null @@ -1,2059 +0,0 @@ -The Project Gutenberg eBook of Determination of The Atomic Weight Of -Cadmium and The Preperation of Certain Of Its Sub-Compounds, by Harry C. -Jones - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Determination of The Atomic Weight Of Cadmium and The Preperation - of Certain Of Its Sub-Compounds - -Author: Harry C. Jones - -Release Date: February 13, 2022 [eBook #67396] - -Language: English - -Produced by: The Online Distributed Proofreading Team at - https://www.pgdp.net (This file was produced from images - generously made available by The Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC -WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS -SUB-COMPOUNDS *** - - - - - -Transcriber’s Notes: - - Underscores “_” before and after a word or phrase indicate _italics_ - in the original text. - Small capitals have been converted to SOLID capitals. - Typographical and punctuation errors have been silently corrected. - The symbol “ī” (small i with macron)was used in place of the numeral - 1 (one) with macron. - The symbol “̅2” (overline + 2) was used in place of numeral 2 with - macron. - - - - - Determination of The Atomic Weight - of Cadmium and The Preparation of - Certain Of Its Sub-Compounds. - - Dissertation, - - Presented to The Board of University Studies - of The - Johns Hopkins University, - - For The Degree of - Doctor of Philosophy, - - By - Harry C. Jones - - 1892. - - - - -_Contents._ - - - Page - Determination of the Atomic Weight of Cadmium 1 - Introduction and Historical Statement 2 - Preparation of Pure Cadmium 22 - The Preparation of Pure Nitric Acid 28 - The Arrangement of Crucibles 30 - The Mode of Procedure 32 - The Weighing 37 - Taring the Crucibles 40 - The Results 42 - Objections to the Method 45 - Advantages of the Method 48 - The Oxalate Method 50 - Preparation of Pure Oxalic Acid 51 - Preparation of Cadmium Oxalate 52 - Mode of Procedure 53 - The Drying and Weighing of the Oxalate 55 - The Results 58 - Advantages of the Method 60 - Disadvantages of the Method 61 - Preparation of Certain Sub-compounds of Cadmium 63 - Historical 64 - The Preparation of Cd₄Cl₇ 66 - The Preparation of Cd₄Br₇ 78 - The Preparation of Cd₁₂I₂₃ 82 - The Preparation of Cadmium Hydroxide and Oxide 82 - Notes on Crystals of Metallic Cadmium 97 - The Cohesion Phenomena of Cadmium 103 - Biographical Sketch 106 - - - - -Acknowledgment. - - -It affords me great pleasure to express my sincere thanks to Professor -Remsen for his instruction and personal supervision during my entire -connection with the University; to Dr. Morse, under whose immediate -guidance the work described in this dissertation was completed; to -Dr. Renouf for valuable assistance in qualitative chemistry and to -Dr. Williams, with whom the branches of mineralogy and geology were -followed as subordinate subjects. - - - - -Determination of the Atomic Weight of Cadmium. - -Introduction and Historical statement. - -A careful examination of the literature on the atomic weight of cadmium -will convince any one that considerable uncertainty yet remains in -reference to this constant. Six experimenters have worked on this -problem but the results of no one of them can be accepted as being more -accurate than those of all others. The value assigned to cadmium varies -from 111.48 to 112.32 on the basis of oxygen = 16. The best work has -apparently been done by von Hauer, Lenssen and Huntington. The results -of these three seem entitled to about equal confidence, yet the figure -obtained by von Hauer differs from that of Huntington by three tenths -of a unit. - -The more prominent difficulties which have been encountered were: - - First. The preparation of cadmium compounds free from all - impurities, and which at the same time were well adapted - to weighing. - - Second. The lack of a thoroughly simple and exact method - for the analysis of cadmium compounds. - - Third. Insufficient care in weighing in many cases whereby - small errors were introduced into the results. - -The methods which have been employed are: - - 1 Conversion of the metal into the oxide. (Stromeyer). - - 2 Conversion of the sulphate into the sulphide. (von Hauer - and Partridge). - - 3 Decomposition of the oxalate to the oxide. (Lenssen and - Partridge). - - 4 Determination of the chlorine in cadmium chloride, by - which the relation between the chloride and metallic silver - was established. (Dumas.) - - 5 Precipitation of the bromine in cadmium bromide as silver - bromide. (Huntington.) - - 6 The conversion of the oxalate into the sulphide. - (Partridge.) - -The different pieces of work will be taken up in chronological order -and briefly considered. - -Stromeyer, Schurigg Journ. 22, 366. 1818, determined the atomic weight -of cadmium a short time after the discovery of the element. He does -not describe his method in detail but established the relation between -cadmium and oxygen to be: - - Cd : O = 100 : 14.352. - - If the atomic weight of oxygen = 16, - ” ” ” ” cadmium = 111.483. - -The very low result as compared with all subsequent work was probably -due to the presence of a small amount of zinc, since the cadmium used -was obtained from zinc ores and no adequate means of separation from -the zinc is described. - -von Hauer, Journ. f. prakt. Chem. 72, 338. 1857. His method consisted -in reducing a weighed amount of cadmium sulphate to the sulphide -in a stream of hydrogen sulphide, under pressure, at an elevated -temperature, and weighing the sulphide. The reduction was shown to be -complete by proving the absence of sulphate in the sulphide. - - 64.2051 grams of cadmium sulphate - gave 44.4491 ” ” ” sulphide. - - If the atomic weight of oxygen = 16, - ” ” ” ” ” sulphur = 32.059, - ” ” ” ” cadmium = 111.935. - -The atomic weight of cadmium calculated as an average of the nine -determinations made using the above values for oxygen and sulphur = -111.94. - - Maximum, 112.121. - Minimum, 111.796. - Mean, 111.940. - -The work of von Hauer is greatly to be preferred to that of Stromeyer. -The large amount of material used in each determination tended to -lessen any experimental error. A very considerable degree of care -seems to have been exercised in purifying the cadmium sulphate. In -determinations 1-5 a different specimen of sulphate was employed from -that in determinations 6-9. The average value found in the first -five determinations = 111.910, in the last four = 111.977. The close -agreement between the results obtained from the different preparations -of the sulphate argues in favor of a fair degree of purity for all the -material. - -The method of weighing the more or less hygroscopic cadmium sulphate is -open to criticism when employed in accurate work. The cadmium sulphate -was placed in an open boat, dried, cooled over sulphuric acid, and -weighed. It was again dried, cooled as before, and weighed. The second -weighing could be quickly accomplished since the approximate weight -was known. The two weighings agreed to within less than a milligram -or a third drying and weighing were made. An error of a milligram -in the weight of the sulphate produced an average error in the atomic -weight of cadmium of about .06. That a discrepancy of greater or less -magnitude was introduced from this source will be readily seen. - -Dumas Ann. Chim. Phys. 55, 158. 1859, determined the relation between -cadmium chloride and the metallic silver required to precipitate the -chlorine. Metallic cadmium was dissolved in boiling hydrochloric acid -and the solution evaporated. The cadmium chloride was fused for five or -six hours in a stream of hydrochloric acid gas. Six determinations were -made. 23.0645 grams of cadmium chloride were equivalent to 27.173 grams -of metallic silver. - - If the atomic weight of silver = 107.93. - ” ” ” ” ” chlorine = 35.45. - ” ” ” ” cadmium = 112.322. - -The atomic weight of cadmium calculated as the average of the six -determinations made, using the above values for silver and chlorine = -112.241. - - Maximum, 112.759. - Minimum, 111.756. - Mean, 112.241. - -The large difference between the results would indicate some -considerable source of error in part or all of the determinations. -The first three determinations were made from a different specimen of -cadmium from the last three. - -In the first three the cadmium used does not seem to have been -purified and the cadmium chloride prepared from it was more or less -tinted brown. In the last three a new specimen of metal was used -which in Dumas’ words could reasonably be considered to be absolutely -pure. The chloride prepared from it was colorless, well crystallized -and perfectly soluble in water. In order to show clearly the wide -discrepancy between the results obtained from the two specimens of -cadmium which were used, the separate determinations are given in -detail. - - At. Wt. - CdCl₂ Ag. Cadmium. - 1 2.369 2.791 112.322 - 2 4.540 5.348 112.347 - 3 6.177 7.260 112.759 - 4 2.404 2.841 111.756 - 5 3.5325 4.166 112.135 - 6 4.042 4.767 112.130 - -The average result of the first three determinations = 112.476. The -average result of the last three determinations = 112.007. From Dumas’ -own statement concerning the purity of the cadmium chloride analyzed, -determinations 4-6 are much to be preferred to determinations 1-3 and -the most probable value from Dumas’ work would be very nearly 112. - -Lenssen Journ. f. prakt. Chem. 79, 281. 1860, regarded the oxalate of -cadmium as well adapted to the determination of the atomic weight of -cadmium. A solution of cadmium chloride which had been purified by -repeated crystallization was treated with an excess of a solution of -pure oxalic acid. The cadmium oxalate formed was filtered off, washed, -and carefully dried in the air at 150° C. until the last trace of -water was removed. 1.5697 grams cadmium oxalate gave 1.0047 grams -cadmium oxide. - - If the atomic weight of oxygen = 16, - ” ” ” ” carbon = 12.003, - ” ” ” cadmium = 112.043. - -The average of the three determinations using the above values for -oxygen and carbon is 112.067. - - Maximum, 112.304. - Minimum, 111.911. - Mean, 112.067. - -The small amount of material used in each determination, the small -number of determinations made, and the rather large difference between -the highest and lowest result are objectionable. There are certain weak -points in the method but to these reference will be made later. - -Huntington, Proc. Amer. Acad. 17, 28. 1882, working with Cooke, made -two series of determinations of the atomic weight of cadmium. In the -first series the relation between cadmium bromide and the silver -bromide formed from it was determined. In the second, the relation -between cadmium bromide and the silver required to precipitate the -bromine. - -The cadmium bromide was prepared by dissolving the carbonate in -hydrobromic acid and subliming the product in a stream of carbon -dioxide. - -In the first series of eight determinations 23.3275 grams of cadmium -bromide were equivalent to 32.2098 grams of silver bromide. - - If the atomic weight of silver = 107.93. - ” ” ” ” ” bromine = 79.95. - ” ” ” ” cadmium = 122.239. - - Maximum, 112.290. - Minimum, 112.169. - -Where the difference between the maximum and minimum value is slight, -the average of the separate determinations agrees closely with the -number found by comparing the total substance used with the total -product obtained. The latter method of calculation seems however to be -preferable. - -In the second series of eight determinations 28.6668 grams of cadmium -bromide were equivalent to 22.7379 grams of silver. - -Using the same values for silver and bromine, the atomic weight of -cadmium = 112.245. - - Maximum, 112.320. - Minimum, 112.180. - -The agreement of the separate determinations with each other is -fairly close and the average of the two series of determinations is -nearly the same. Huntington took great care in the purification of -his material and in the carrying out of his method, which are strong -arguments in favor of his work, yet his method is not as simple as -could be desired where the nature of the work demands the greatest -possible accuracy in all details and it also appears to be subject to -some of the errors common to ordinary analytical operations. - -Partridge. Amer. Journ. Science XL, 377. 1890. Methods: 1ˢᵗ. -Decomposition of the oxalate to the oxide. 2ⁿᵈ. Reduction of the -sulphate to the sulphide. 3ʳᵈ. Conversion of the oxalate into the -sulphide. As an average of the determinations made by each method -Partridge gives: - - 1ˢᵗ series, atomic weight of cadmium = 111.8027. - 2ⁿᵈ ” ” ” ” ” = 111.7969. - 3ʳᵈ ” ” ” ” ” = 111.8050. - -An excellent agreement between results obtained by different methods[1]. - -That this very close agreement is only apparent has been shown by -Clarke. He has found that the above calculations are based on the -assumption that the atomic weight of carbon = 12, and that of sulphur -= 32 when oxygen = 16. There seems to be little justification for -this rather arbitrary selection by Partridge since the most refined -work shows that whole numbers do not express the most probable atomic -weights of carbon and sulphur in a system where oxygen = 16. - -[1] Amer. Chem. Journ. 13, 34. 1891. - -The atomic weight of cadmium calculated from the total material used -and the total product found in each of the three series is: - - O = 16. C = 12. S = 32. At.Wt.Cd. - 1ˢᵗ series, CdC₂O₄ : CdO = 12.66368g. : 8.10031g. 111.805. - 2ⁿᵈ ” CdSO₄ : CdS = 15.93505g. : 11.02691g. 111.786. - 3ʳᵈ ” CdC₂O₄ : CdS = 16.85228g. : 12.12906g. 111.806. - difference, 0.020. - - O = 16. C = 12.003 S = 32.059 At.Wt.Cd. - 1ˢᵗ series, CdC₂O₄ : CdO = 12.66368g. : 8.10031g. 111.816. - 2ⁿᵈ ” CdSO₄ : CdS = 15.93505g. : 11.02691g. 111.727. - 3ʳᵈ ” CdC₂O₄ : CdS = 16.85228g. : 12.12906g. 111.610. - difference, 0.206. - -As Clarke has pointed out when those values are chosen for carbon -and sulphur which are founded on the best experimental evidence the -agreement between the different series of results as calculated by -Partridge is somewhat modified. - -I have repeated the work on which series I is based and would call -attention to the following points in which it appears to have been -experimentally defective. - - 1 The metal was only distilled twice in a vacuum. It has - been found in this laboratory that perfectly pure - cadmium or zinc can be prepared only by repeated - distillations, each one being carried on slowly to allow - the impurities to separate by means of their difference - in volatility. - - 2 The supposed mixture of metal and oxide resulting from - the decomposition of the oxalate was only moistened with - a few drops of nitric acid in order to reoxidize any - reduced metal. Unless the entire mass of metal and oxide - was dissolved there would be danger of the presence of - free undissolved metal which would possess an appreciable - vapor-tension below the temperature of decomposition of - cadmium nitrate. An appreciable loss in weight resulting - from a distillation of the metal out of the crucible might - easily result. - - 3 It seems very probable that the cadmium nitrate was - not heated sufficiently to remove all traces of the - oxides of nitrogen. I have found that this could only be - accomplished by long continued heating. Constant weight - was not sufficient to have decided this point since it was - also found that this could be reached short of complete - decomposition, if the temperature was too low to remove - the last traces of these oxides. Some very delicate test - for such oxides should have been applied at the end of - each experiment. - -The following table contains a summary of the results thus far obtained. - -When two values are given for one series of determinations, the first -is calculated from the total material used and the total product found, -the second is an average of the results of the separate experiments. -Oxygen is taken as 16 throughout. - - Date. Investigators. At.Wt.Cd. - 1818, Stromeyer, 111.483 - - 1857, von Hauer, 111.935 } - 111.940 } - - 1859, Dumas, 112.322 } - 112.241 } - - 1860, Lenssen, 112.043 } - 112.067 } - - 1882, Huntington, 1ˢᵗ series 112.239 - ” 2ⁿᵈ ” 112.245 - - 1890, Partridge, 1ˢᵗ series 111.805 - ” 2ⁿᵈ ” 111.786 - ” 3ʳᵈ ” 111.806 - -In the above calculation of Partridge’s results C = 12. S = 32. In the -following carbon is taken as 12.003 and sulphur is 32.059. - - 1890, Partridge, 1ˢᵗ series 111.816 - ” 2ⁿᵈ ” 111.727 - ” 3ʳᵈ ” 111.610 - -After a careful examination of the methods available it becomes evident -that no one of them was _per se_ as accurate as the method employed -by Morse and Burton,[2] for the determination of the atomic weight of -zinc, and more recently by Burton and Morse,[3] for the determination -of the atomic weight of magnesium. The method of work was to prepare -pure metallic cadmium, to convert a weighed portion of the metal -into nitrate by means of pure nitric acid, to decompose the nitrate -completely to oxide and to weigh the oxide. - -[2] Amer. Chem. Journ. X, 311. - -[3] ib. XII, 219. - - - - -Preparation of Pure Cadmium. - - -The work of preparing pure cadmium was begun more than two years ago -by Mr. W. V. Metcalf with Dr. H. N. Morse. I wish to express here -my sincere thanks to him for the material with which the following -determinations were made. The cadmium used by him was obtained from -Schuchart and marked “Met. prss. (galv.) redus.” - -The method of purification by fractional distillation in a vacuum, was -essentially that employed by Morse and Burton for the purification of -metallic zinc. - -The distillation was carried out in hard glass tubes of the size of -ordinary combustion tubing. - -[Illustration: FIG. 1.] - -Fig. 1. represents such a tube. A hard glass tube, 600-700 mm. -in length, was closed at one end and about 130 grams of cadmium -introduced. The walls of the tube were heated and indented at the two -points a, and b, with a red-hot file, dividing the tube into three -sections marked A, B and C. The open end of the tube was drawn out, -bent, and attached to a Sprengel air-pump by means of a rubber tube. - -The joint was tied tightly with waxed cord and surrounded by mercury. -When the manometer indicated that the tube was exhausted, it was -gradually heated by the combustion furnace in which it rested. The -metal in A melted and distilled slowly into the front portion of the -tube. Most of it condensed in B, while a small part, together with -any more volatile impurity, collected in C which was kept cooler than -the remainder of the tube. When about four-fifths of the metal placed -in A had distilled over, the tube was very slowly cooled. When cold, -the tube was broken open, the portions in A and C being rejected in -every case, while the metal was recovered from B in the form of a -bar resting on the bottom of the tube, together with some crystal -aggregates, suspended from the top and sides. A few crystal individuals -were secured but the measurement of these will be considered later. The -metal separated from the glass with a highly lustrous surface and did -not attack the glass in the least. - -The first distillation was effected in a tube bridged as represented -in Fig. 1, but drawn out at each end. The original cadmium powder was -heated in the tube in a stream of pure hydrogen gas, for the purpose -of obtaining the metal in the form of bars, and to reduce any cadmium -oxide contained in the powder. - -Six distillations were made in a vacuum. In the first, 630 grams of -metal were used being distilled in quantities of about 130 grams -each. At the end of the sixth distillation, there were about -100 grams of pure cadmium at disposal. In the fifth and sixth -distillations, the metal was heated just above the melting point for -from twenty to twenty-four hours, before being forced over into the -middle portion of the tube. By this means all the remaining traces of -the more volatile arsenic were driven into the front part of the tube -and separated from the cadmium. - - -The distillations. - -The residue represents the undistilled portion remaining in A. The -distillate, the material obtained from B after the distillation was -completed. The coating, the substance which condensed in C. - - Residue, Cd, Pt, Zn,? As?. - Distillation I Distillate, Cd, Zn,? As? - Coating, Cd, Zn,? As?. - - Residue, Cd, Zn?, As?. - Distillation II Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd, Zn?, As?. - Distillation III Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd, Zn?, As?. - Distillation IV Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd. - Distillation V Distillate, Cd. - Coating, Cd, As?. - - Residue, Cd. - Distillation VI Distillate, Cd. - Coating, Cd. - -The distillate from the last distillation was examined -spectroscopically by Professor Rowland and found to be free from all -traces of impurity which would be detected by that method. The chemical -test for arsenic was more delicate than the spectroscopic and this -failed to reveal a trace. - - -The preparation of pure nitric acid. - -The method of preparing the pure acid and of preserving and -transferring it was the same as adopted by Morse and Burton in their -work on the atomic weight of zinc. - -[Illustration: FIG. 2.] - -The simple form of apparatus is represented in fig. 2. A large platinum -vessel containing fragments of ice was supported on a smaller platinum -dish, from which it was separated by hooks of large platinum wire. The -acid was distilled from a small flask as represented in the drawing. - -The purest nitric acid which could be obtained was diluted with about -an equal volume of water. The vessel containing the acid was heated -very gently that the distillation might take place without boiling. -The dilute acid condensed on the cold surface of the larger dish and -collected in the smaller, in which it was preserved until used. This -acid gave no residue on evaporation. - - -The arrangement of crucibles. - -[Illustration: FIG. 3.] - -The arrangement of the crucibles in which the determinations were -made is represented in fig. 3. 1 is a small porcelain crucible, (00) -from the exterior and lid of which the glaze had been removed by -hydrofluoric acid. The lid was separated from the crucible by hooks -made from thick platinum wire, to allow free communication between the -contents of the crucible and the external air. This would facilitate -the outward diffusion of the oxides of nitrogen when liberated from -the nitrate. 2 is an uncovered porcelain crucible (no. II) in which 1 -was placed. From the exterior the glaze had been removed to prevent -the crucible from adhering to the unglazed porcelain scorifier on -which it rested. The exterior was carefully brushed after treatment -with hydrofluoric acid to remove all loose particles adhering to its -surface. Crucibles 1 and 2 were not separated during a determination. - -3 is a nickel crucible about two and a half inches in diameter. The -porcelain crucibles were not allowed to touch the nickel at any point. -The nickel crucible was covered by a lid of nickel. - - -The mode of procedure. - -A piece of cadmium weighing from two to three grams was cut from the -bar of the metal by means of a steel chisel. This was seized with steel -forceps and filed with a hard steel file to about one half the original -weight. Care was taken to remove the entire exterior portion of the -metal which had come in contact with the chisel or had stood exposed to -the air. The plug of metal was then carefully brushed and examined with -a lens to insure the removal of all loose particles from the surface. - -Crucibles 1 and 2 having been brought to constant weight against -their tare, were ready for use. The piece of cadmium was weighed and -placed in 1. An excess of pure nitric acid was added and a gentle heat -applied until all the metal had dissolved. This required from twenty -to forty hours. - -A sand-bath was constructed by placing a large porcelain crucible in -an iron crucible and filling the intervening space with sand. The pair -of crucibles (1 and 2) was placed in the porcelain crucible and the -contents evaporated to dryness by warming very carefully at first and -gradually increasing the temperature. The pair of crucibles was then -transferred to a bath constructed as the above where iron filings took -the place of sand. This was heated by a single burner until the nitrate -was all decomposed when a triple burner was added and finally two -for six or eight hours. This was not sufficient to effect complete -decomposition. When cold, the pair of crucibles was placed in the -nickel crucible as represented in fig. 3 and sharply heated over a -blast-lamp for several hours. This completed the decomposition of the -nitrate and the removal of the last traces of oxides of nitrogen. - -During the blasting the lid on crucible 3 was raised a little to one -side to allow free access of air. The nickel crucible was forced -tightly into a hole cut in the center of an asbestos board about -ten inches in diameter, to prevent any reducing gases from the lamp -entering the crucibles while hot. This was the same arrangement as was -used by Partridge[4]. - -[4] Amer. Journ. Science XL, 379. - -It was found that the final decomposition of the nitrate could not -be effected in a muffle furnace as with zinc, since at very high -temperatures cadmium oxide attacked the porcelain with great energy and -injured the crucibles. - -The decomposition of the nitrate was shown to be complete not by -constant weight alone, but by testing for oxides of nitrogen with -starch paste rendered extremely sensitive with potassium iodide. That -the test should be reliable, Morse and Burton have pointed out that all -the reagents used must be free from oxidizing agents. The presence of -iodate in the iodide is especially to be avoided. This was removed by -boiling the solution with zinc amalgam. Air was removed from all the -solutions by boiling. - -When the starch-potassium-iodide solution had been prepared as -sensitive as possible, a portion of it was treated with a little -hydrochloric acid, to determine if any iodine was liberated. If no -coloration was observed the cadmium oxide was added. It dissolved in -the hydrochloric acid and if any oxides of nitrogen were present they -would have revealed themselves by the liberation of iodine and a blue -coloration of the starch paste. - -In no one of the ten determinations was the slightest coloration -detected. - -An equal volume of nitric acid was added to the pair of crucibles used -as a tare as to those containing the determination, and they were -heated in exactly the same manner and for the same length of time. - -The crucibles containing the cadmium oxide were heated over the -blast-lamp for an hour, weighed against their tare, reheated, again -weighed, and this continued until there was no further change in -weight. Usually from two to four hours heating over the blast-lamp was -sufficient to completely decompose the nitrate. The test for oxides of -nitrogen was then applied. - -I found that practically constant weight could be reached short of -compete decomposition, at a temperature below that necessary to -transform all the nitrate into the oxide. This necessitated the final -test for oxides of nitrogen. - - -The Weighing. - -The balance used was a No. 8 long-armed one, made by Becker and Sons. -It was supported by iron brackets fastened to one of the foundation -walls of the laboratory. - -Here it would be subjected to the least jar and was also well protected -from air currents. All weighings were made between the hours of one and -five in the morning when the surroundings were as quiet as could be -desired. A very slight disturbance was detected by the vibrations on -the surface of a cup of mercury placed conveniently between the pans. - -That the presence of the operator might not produce any change in the -balance during the weighing, he closed the room, placed the light above -and behind his head and took his position in front of the balance at -least an hour before making a weighing. When his presence no longer -affected the balance (which was shown by the zero point remaining -constant in a series of determinations) the weighing was begun. The -method of weighing by vibrations and upon both pans was employed -throughout. - -Each zero point was taken as the mean of three closely agreeing zero -determinations; each one of the three being the mean of seven readings. -The zero of the balance empty was determined just before and after -each weighing to detect any change in its position. Usually none was -observed. The sensibility of the balance was taken at each weighing -with the weights used at that weighing. A displacement of the zero -point about six divisions of the ivory scale was effected by the -addition of one milligram. - -The weights had been especially adjusted and were carefully compared -with each other before using. - -Weighing by tares was adopted as preferable to any other method. By -this means all errors resulting from changes in the moisture of the air -were avoided and any errors which might have been introduced by heating -or manipulating the crucibles would be counteracted by treating the -tare in exactly the same manner. - - -Taring The Crucibles. - -A pair of crucibles (1 and 2 in the figure) was selected and treated as -described. Another pair about the same size but a little lighter was -prepared in exactly the same way. Each pair was placed in the nickel -crucible and heated by means of the blast-lamp for half an hour. - -After cooling in desiccators, both pairs of crucibles where placed in -the closed balance until no longer affected by the moisture of the -air, which was also dried by calcium chloride. The tare was brought to -within one tenth of a milligram of the weight of the crucibles against -which it was being tared, by adding fragments of porcelain obtained -from another crucible of the same composition. The difference in weight -between the tare and its mate was then accurately ascertained. - -Each pair of crucibles was again placed in the nickel crucible and -blasted for half an hour. They were then reweighed, to determine if the -difference in weight previously found had remained constant. In no case -was any change detected, yet this precaution was always taken. - - -The Results. - -The following table contains the results of ten successive -determinations. - - At. Wt. Cd. At. Wt. Cd. - Wt. of Cd. Wt. of CdO. (O = 16) (O = 15.96) - I 1.77891 2.03288 112.070 111.790 - II 1.82492 2.08544 112.078 111.798 - III 1.74688 1.99626 112.078 111.798 - IV 1.57000 1.79418 112.053 111.773 - V 1.98481 2.26820 112.061 111.781 - VI 2.27297 2.59751 112.059 111.779 - VII 1.75695 2.00775 112.086 111.806 - VIII 1.70028 1.94305 112.059 111.779 - IX 1.92237 2.19679 112.083 111.803 - X 1.92081 2.19502 112.078 111.798 - ------- ------- ------- ------- - Mean, 112.0705. 111.7905. - Maximum, 112.086. 111.806. - Minimum, 112.053. 111.773. - Difference, .033. .033. - -Calculating the atomic weight of cadmium from the total amount of metal -used and oxide found, we have: - - At. Wt. of Cd. At. Wt. of Cd. - (O = 16) (O = 15.96) - 112.0706. 111.7904. - -These results agree more closely with those of von Hauer and Lenssen -than with those of any other experimenter. The following table gives -a comparison of the work of these investigators with that herein -described: - - von Hauer. Lenssen. Work here described. - 9 determinations. 3 determinations. 10 determinations. - (O = 16) (O = 16) (O = 16) - Mean 111.940 112.067 112.0705 - Max. 112.121 112.304 112.086 - Min. 111.796 111.911 112.053 - Diff. .325 .393 .033 - -A difference of three or four tenths of a unit between the different -results of a series leaves considerable doubt as to the accuracy of the -method employed and to the value obtained. - -The figure selected by Ostwald,[5] as most probable for the atomic -weight of cadmium is 112.08. This is the mean of the results on von -Hauer and Huntington. My own work leads me to believe that this number -is very close to the true value when oxygen is taken as 16. - -[5] Lehrb. d. Allg. Chem. I, 60. - - -Objections to the method. - -Marignac[6] offered the objection to this method for determining the -atomic weight of zinc that the zinc oxide dissociated when heated in -platinum over the blast-lamp. The same objection might be urged against -this method for determining the atomic weight of cadmium, had it not -been shown that the objection does not hold for zinc[7]. What took -place was a reduction of the zinc oxide by the highly heated hydrogen -which passed through the hot platinum. - -[6] Archives des Sciences Phys. et Nat. (3) 10, 193. - -[7] Amer. Chem. Journ. X, 148. - -It was shown that zinc oxide can be heated in a platinum vessel in a -muffle furnace, to the melting point of steel, without undergoing any -dissociation, or in any wise losing in weight. This source of error was -avoided by using porcelain vessels, which were not brought into contact -with the free flame. - -The statement of Marignac that the oxide of zinc derived from the -nitrate retains oxides of nitrogen even when heated to the temperature -at which it begins to undergo dissociation, was shown by the same -authors to be without foundation. The basis of this objection is -doubtless to be found in the imperfect method of testing for such -oxides. - -It might be urged as an objection to this method that the difference -in weight between the metal and oxide is not very great, therefore any -error in weighing would be multiplied in the result. At first sight -this objection may appear valid, but since the substances weighed were -so well adapted to that purpose and the weighings could be made with -such a high degree of accuracy no appreciable error could have resulted -from this source. - -A crucible with its contents was repeatedly weighed against its tare -and weights to ascertain the difference between successive weighings -under the conditions employed. A number of weighings agreed to .00002 -gr. and in some instances to half this amount. - - -Advantages of the Method. - - 1 The great advantage of the method is its extreme - simplicity. From the beginning of an experiment until - the end the contents of the crucible are not brought - into contact with any foreign substance. By this means - small errors resulting from incomplete precipitation, - and filtration and all other errors incident to ordinary - processes of analysis were avoided. - - 2 The nature of the metal and its oxide rendered them well - adapted to weighing. The specific gravity of the metal and - oxide approached so closely to that of the weights, that - it was unnecessary to reduce the weighings to a vacuum - standard. - - 3 The advantages derived from weighing by tares have been - pointed out. - - 4 The closely agreeing results speak strongly in favor of - the accuracy of the method. - - - - -The Oxalate Method. - - -The method consists in taking a weighed amount of cadmium oxalate, -decomposing it by heat, when a mixture of oxide and metal are said -to be formed, dissolving this mixture in nitric acid, converting the -nitrate into oxide and weighing the oxide. - -Lenssen[8] obtained results by this method which agree very closely -with those recorded in the earlier part of this dissertation. - -Working with the same method, Partridge[9] arrived at a value about one -fourth of a unit lower than that of Lenssen. - -[8] Journ. f. prakt. Chem. 79, 281. - -[9] Amer. Journ. Science XL, 377. - -It appeared desirable that this method should be repeated with the -greatest care to ascertain what result it would give under the most -favorable conditions. - -Having a supply of pure cadmium it was necessary to prepare pure oxalic -acid. - - -Preparation of Pure Oxalic Acid. - -The commercial acid was crystallized three times from cold water to -separate it from acid oxalates. It was then boiled for two days with -a 15 per cent solution of hydrochloric acid, to remove any mineral -matter present. The acid which crystallized from the hydrochloric acid -solution was recrystallized twice from hot, redistilled alcohol and -twice from pure ether. It was finally boiled with water to decompose -any ethyl oxalate and twice crystallized from pure water. The acid was -dried in the air at ordinary temperatures. This acid left no residue on -ignition. - - -Preparation of Cadmium Oxalate. - -A piece of cadmium was dissolved in pure nitric acid. On carefully -evaporating the solution cadmium nitrate was obtained. Twenty-five -grams of the nitrate were dissolved in 750 c.c. of redistilled water. -Somewhat less than an equivalent of the oxalic acid was dissolved in -an equal volume of water, and slowly added to the solution of the -nitrate with constant shaking. A little less than an equivalent of -oxalic acid was used to avoid any tendency to form acid oxalates. -Cadmium oxalate was precipitated on standing a few minutes as a white -crystalline compound, well adapted to washing. The oxalate was filtered -off and washed until the wash water was free from all traces of nitric -acid. It was then washed ten times with water which had been twice -redistilled and dried in an air-bath for twenty hours at 150°C. - -The arrangement of the crucibles which were weighed was in all respects -like that in the preceding method. - - -Mode of Procedure. - -The crucibles were heated, tared, and weighed exactly as in the -preceding method. The oxalate was weighed in ground-stoppered weighing -tubes from which it was transferred to the inner of the two porcelain -crucibles. The pair of crucibles, (1 and 2 fig. 3) was placed in a -third porcelain crucible and the whole system introduced into an -upright air-bath. The outer crucible was supported on a porcelain -triangle about an inch from the bottom of the bath and was not allowed -to touch its walls at any point. The top of the bath was covered with a -sheet of iron over which was placed an asbestos board. The exterior was -also covered with a lining of asbestos. A thermometer was introduced -well into the bath. The temperature was allowed to rise slowly until -the oxalate began to show a brown color around the edge. From this -stage the temperature was kept as low as possible in order to effect -the decomposition. When the oxalate was decomposed the bath was allowed -to cool and the contents of the crucible completely dissolved in nitric -acid. The nitrate was evaporated to dryness and decomposed as in the -method first described. The end of the decomposition was determined in -the same manner and the oxide, free from all impurities, weighed. - - -The Drying and Weighing of the Oxalate. - -It was necessary to dry the oxalate before weighing from fifteen to -twenty hours at 150°C. in addition to the twenty hours drying of the -whole preparation. At this temperature the last traces of moisture were -removed by prolonged heating. - -The weighing of the oxalate was made in the weighing glasses in which -it was dried. Two of these glasses had been previously tared against -each other, using the lighter as the tare and adding fragments of -glass to it until the difference in weight was a small fraction of -a milligram. The oxalate having been dried to constant weight, was -weighed. It was then poured as carefully and completely as possible -from the weighing glass into the crucible and the glass again weighed -against its tare. The difference in the two weights gave the amount of -oxalate. The glass and its tare were dried and reweighed to determine -if the few milligrams of oxalate adhering to the walls of the glass -had absorbed any moisture during the transfer of the oxalate. In one -experiment a slight difference was detected when a second drying and -weighing were made. - -The weight of the cadmium oxalate as obtained from the balance was -corrected for the difference in specific gravity between the cadmium -oxalate and the weights. - - -The Results. - - At. Wt. At. Wt. At. Wt. At. Wt. - Cd. Cd. Cd. Cd. - (O=16) (O=16) (O=15.96) (O=15.96) - (C=12.001) (C=12.003) (C=11.971) (C=11.973) - CdC₂O₄ CdO - I 1.53937 .98526 112.026 112.033 111.746 111.753 - II 1.77483 1.13582 111.981 111.988 111.701 111.708 - III 1.70211 1.08949 112.049 112.056 111.769 111.776 - IV 1.70238 1.08967 112.051 112.058 111.771 111.778 - V 1.74447 1.11651 112.019 112.026 111.739 111.746 - ------- ------- ------- ------- - Mean, 112.025 112.032 111.745 111.752 - Maximum, 112.051 112.058 111.771 111.778 - Minimum, 111.981 111.988 111.701 111.708 - Difference, .070 .070 .070 .070 - -The values assigned to carbon in the last two columns were found thus-- - - When O = 16, C = 12.001, when O = 15.96, C = 11.971. - ” O = 16, C = 12.003, ” O = 15.96, C = 11.973. - -Calculating the atomic weight directly from all the oxalate used and -oxide found it would give: - - At. Wt. Cd. At. Wt. Cd. At. Wt. Cd. At. Wt. Cd. - (O = 16) (O = 16) (O = 15.96) (O = 15.96) - (C = 12.001) (C = 12.003) (C = 11.971) (C = 11.973) - - 112.025. 112.032. 111.745. 111.752. - -There seems about equal evidence for the two values assigned to carbon -when oxygen = 16. The value of cadmium as given by this method is -therefore 112.025 or 112.032. - -As will be seen at a glance this figure agrees much more closely with -that of Lenssen than with that of Partridge. - - Lenssen Partridge My work - 112.043. 111.816. 112.025 or - 112.032. - -It also agrees fairly well with the figure 112.0706 which I obtained by -the first method described. - - -Advantages of the Method. - -The method possesses no advantage whatever over the one which involves -starting with the element itself. The oxalate can however be obtained -pure having pure metal. The salt is of definite composition when -perfectly dry. - -The method as carried out avoided the contact of any foreign material -with the salt after it was weighed. - - -Disadvantages of the Method. - - 1 The avidity with which the dried oxalate takes up - moisture from the air is an objection to its use for the - determination of atomic weights. Even with the greatest - care there is a slight element of uncertainty introduced - from this source. - - 2 The oxalate is stated to decompose into a mixture of - the oxide and metal. The temperature required for this - decomposition is somewhat higher than the melting point - of cadmium. The metal heated above its melting point - possesses a vapor-tension and loss in weight must result, - whatever precaution is taken in heating. This is the - probable explanation why the results obtained by this - method are lower than those of the preceding. - -A comparison of the two methods leads me to attach much more importance -to the results of that one which establishes the relation between -cadmium and cadmium oxide directly and I therefore regard the atomic -weight of cadmium as very closely expressed by the figure 112.07 when -oxygen = 16. - - - - -Preparation of Certain Sub-compounds of Cadmium. - -Historical. - -Cadmium acts so generally as a bivalent element that it is usually -regarded as entering into combination only where it can play this rôle. -The only compound described, in which it has apparently a lower valence -than two, was prepared by Marchand[10]. It was obtained by heating -cadmium oxalate to the melting point of lead when a green powder -remained behind which resembled chromium oxide. When heated on the air -it appeared to be decomposed into metal and oxide. When treated with -mercury the compound was not altered. An analysis showed it to have the -composition represented by the formula Cd₂O. - -[10] Pogg. Ann. XXXVIII, 143. - -A. Vogel[11] has shown that the green powder described by Marchand -consists of a mixture of the metal and oxide. When this mixture is -treated with dilute acetic acid the metal remains behind as microscopic -glistening globules. The lower the temperature at which the oxalate is -decomposed the more oxide and the less metal were found in the product. - -There was then no compound known in which cadmium acted as if its -valence was less than two when this work was undertaken. - -That it may act with a greater valence was shown by R. Haafs[12]. He -found that when zinc hydroxide was treated with hydrogen dioxide -certain compounds of zinc and oxygen were formed containing more oxygen -than the normal oxide ZnO. The close resemblance between zinc and -cadmium led him to try the same reaction with cadmium. Hydrogen dioxide -was accordingly allowed to act on cadmium hydroxide and the resulting -product analyzed. There were formed Cd₅O₈, Cd₃O₅ and Cd₄O₇. In no case -was the compound CdO₂ obtained. These compounds are described as fairly -stable even at a hundred degrees. - -[11] Jahrb. 1855, 390. - -[12] Ber. 1884, 2249. - - -The Preparation of Cd₄Cl₇. - -When anhydrous cadmium chloride is heated with metallic cadmium in a -vacuum, or in an atmosphere of nitrogen, to the fusing point of the -chloride, the molten chloride quickly assumes a garnet red color. -In order to investigate this phenomenon a quantity of the chloride -was prepared by dissolving the redistilled metal in an excess of -hydrochloric acid, evaporating the chloride to dryness on a water -bath, and finally removing the water of crystallization by heating in -a current of dry hydrochloric acid gas. The heating was effected by -placing the chloride in a long platinum boat, which was shoved into a -large glass tube, through which was passed a current of the acid gas. -The tube was heated by means of a combustion furnace and the chloride -kept in the molten condition for two or three hours. By this means -a perfectly white crystalline chloride of the composition CdCl₂ was -obtained, free from water or oxychloride. - -The chloride and an excess of metal were placed in a long-necked flask -of hard glass and after the displacement of the air by nitrogen, heated -to the melting point of the chloride. The liquid chloride attained its -maximum depth of color in a few minutes, nevertheless the heating was -continued for five hours. When the temperature was allowed to rise much -above the melting point of the chloride the red substance underwent -decomposition and globules of metal collected upon the walls of the -flask. For this reason no more heat was applied than was just necessary -to keep the contents of the flask in a liquid condition. During the -very gradual cooling of the flask it was shaken gently in order to -facilitate the sinking of any metal, which might be mechanically -retained by the chloride. - -On cooling, the solidified mass possesses a slightly greenish tint -which disappeared when cold, the substance having then a grayish white -color and a cleavage resembling that of talc or brucite. When examined -under the microscope it was found to be perfectly homogeneous and -free from metal. It gave no metallic streak when rubbed between agate -surfaces. - -An analysis of the first preparation showed the following composition; - - Amount of chloride used .33541 gr. - ” ” cadmium found .21559 ” - ” ” chlorine ” .11943 ” - - Cadmium. Chlorine. - 64.27 per cent. 35.61 per cent. - -These proportions are nearly those of a compound having the composition -Cd₄Cl₇, in which the calculated percentages are: - - Cadmium. Chlorine. - 64.34 35.66 - - (Foot note). In the paper in the American Chemical Journal - XII, 488, which records this work the analyses and - percentages were calculated on the basis of the atomic - weight of cadmium = 111.7. Although my work since this date - has shown that 112.07 is the true value, yet I think it - preferable to use the old number here since the changes to - be introduced would be very slight and the same results are - thereby kept uniform in the two publications. - -In order to determine whether the close approximation to definite -atomic proportions might not be accidental, the material was reheated -with an excess of the metal for twenty hours. The product was analyzed. - - Amount of chloride used 1.45970 gr. - ” ” cadmium found .93904 ” - ” ” chlorine ” .52329 ” - - Cadmium. Chlorine. - 64.33 per cent. 35.85 per cent. - -A second preparation of the substance was made in all respects like the -first. Two analyses were made. - -First Analysis: - - Amount of chloride used .61010 gr. - ” ” cadmium found .39235 ” - ” ” chlorine ” .21725 ” - - Cadmium. Chlorine. - 64.31 per cent. 35.61 per cent. - -Second Analysis: - - Amount of chloride used .20616 gr. - ” ” cadmium found .13266 ” - ” ” chlorine ” .07352 ” - - Cadmium. Chlorine. - 64.35 per cent. 35.66 per cent. - -A third preparation was made like the first and second and analyzed. - -Analysis: - - Amount of chloride used .2832 gr. - ” ” cadmium found .18244 ” - ” ” chlorine ” .10123 ” - - Cadmium. Chlorine. - 64.42 per cent. 35.74 per cent. - -When the new substance is heated it fuses to a red liquid and then -breaks up into metal and the chloride of cadmium. Its reactions are in -general those of a strong reducing agent. Treated with nitric acid, -oxides of nitrogen are liberated. With dilute hydrochloric, sulphuric -and acetic acids it gives free hydrogen. In the presence of dilute -acids it reduces mercuric to mercurous chloride, or to metallic mercury. - -Three determinations of the reducing power of the substance were made -with a freshly prepared specimen, by dissolving weighed portions in -hydrochloric acid and measuring the hydrogen liberated. - -The following results were obtained: - - Hydrogen found. Hydrogen calculated - for Cd₄Cl₇. - 1ˢᵗ determination 15.67 c.c. 15.65 c.c. - 2ⁿᵈ ” 11.80 c.c. 11.82 c.c. - 3ʳᵈ ” 23.00 c.c. 23.03 c.c. - -An examination of the analyses shows beyond question that the -substance formed by the action of metallic cadmium on the molten -anhydrous chloride is of definite composition. The proportion of -cadmium to chlorine could not be changed even when the substance was -heated with the metal for twenty hours, while a very short time was -sufficient for its formation when the metal and chloride were melted -together. - -It may be possible that a substance possessing these properties is -not a definite chemical compound but a mixture of cadmous and cadmic -chlorides or a solution of one in the other. - -If it were a solution it is difficult to see why the composition of the -solution should be so constant, since the solubility of a substance -is generally altered by a change in temperature. The different -preparations were not made at exactly the same temperature yet the -composition of the different preparations was the same. - -If the substance was a mixture of the two chlorides, when treated with -water the cadmic chloride would most probably dissolve directly leaving -the cadmous chloride to be acted upon by the water. The decomposition -by water will however be seen not to be as simple as would be expected -under these conditions. - -From the above considerations it appears highly probable that the -substance is a definite chemical compound of cadmic and cadmous -chlorides. If cadmic chloride can form a chemical compound with the -chloride of another element there appears to be no reason why it -should not form a compound with another chloride of cadmium, as with -cadmous chloride. - - -The preparation of Cd₄Br₇. - -The anhydrous bromide of cadmium was prepared by dissolving the -carbonate in an aqueous solution of hydrobromic acid, evaporating -the bromide to dryness on the water bath and heating the residue in -a current of dry hydrobromic acid gas. When the bromide was heated -with an excess of the metal in an atmosphere of nitrogen it conducted -itself in general like the chloride. When the molten bromide and the -metal came in contact the salt quickly became deep red in color. -After heating for some time considerable dissociation was produced by -raising the temperature. This was more apparent in the preparation of -the bromide than with the chloride. On cooling, the mass possessed -a greenish tint which disappeared when cold, the bromide then being -very nearly the same color as the corresponding chloride. Also like -the chloride it appeared to be homogeneous and free from metal. Two -determinations of cadmium and two of bromine were made, using the -product as soon as prepared. - -First determination of cadmium: - - Amount of substance used .3736 gr. - ” ” cadmium found .16658 ” - - Cadmium. - 44.59 per cent. - -Second determination of cadmium: - - Amount of substance used .35930 gr. - ” ” cadmium found .16013 ” - - Cadmium. - 44.57 per cent. - -First determination of bromine: - - Amount of substance used .66640 gr. - ” ” bromine found .36953 ” - - Bromine. - 55.45 per cent. - -Second determination of bromine: - - Amount of substance used .56035 gr. - ” ” bromine found .31085 ” - - Bromine. - 55.47 per cent. - -The percentage of cadmium and bromine found agrees very closely with -that of a compound of the formula Cd₄Br₇. The relation of cadmium to -bromine in this would be: - - Cadmium. Bromine. - 44.44 per cent. 55.56 per cent. - -When this compound was heated for a long time with an excess of the -metal its composition was not appreciably changed. - -The compound Cd₄Br₇ is a strong reducing agent: giving with nitric -acid oxides of nitrogen, with dilute hydrochloric, sulphuric or acetic -acid, free hydrogen, and with mercuric chloride, mercurous chloride or -metallic mercury. The action of water on the bromide by means of which -cadmous hydroxide was formed, was not studied as carefully as with the -chloride but appeared to be essentially the same. - - -The Preparation of Cd₁₂I₂₃. - -Cadmic iodide was prepared in the same manner as the bromide. It was -dried in a stream of hydriodic acid gas at as low temperature as -possible to lessen the decomposition of the hydriodic acid. When the -anhydrous iodide was heated with an excess of metal in an atmosphere of -nitrogen the red color of the iodide became intensified. Heating was -continued until there was evidence of dissociation, which, under the -same conditions, was less marked than with the chloride and much less -than with the bromide. Owing to the high specific gravity of the iodine -compound some difficulty was experienced in obtaining a preparation -free from metal. This difficulty was finally overcome by keeping -the material just above its melting temperature for a long time and -constantly jarring the flask. During the process of cooling a decidedly -greenish tint was observed which disappeared as the process was -continued. When cold the substance resembled the chloride and bromide. -Two determinations of cadmium were made in the first preparation. - -First determination: - - Amount of substance used .55540 gr. - ” ” cadmium found .17456 ” - - Cadmium. - 31.43 per cent. - -Second determination: - - Amount of substance used .47535 gr. - ” ” cadmium found .14980 ” - - Cadmium. - 31.51 per cent. - -As these results did not correspond to the composition represented by -the formula Cd₄I₇, which our experience with the chloride and bromide -had led us to expect, we reheated the material for several hours with -an excess of the metal. Two analyses of the product gave: - - Cadmium. Iodine. - 31.44 per cent. 68.65 per cent. - 31.39 68.68 - -showing that the iodide had taken up during the first heating all the -metal which it could retain. The analytical results suggest the formula -Cd₁₂I₂₃, in which the calculated percentages are: - - Cadmium. Iodine. - 31.53 per cent. 68.47 per cent. - -In its conduct towards dilute hydrochloric and acetic acids and water -the substance behaves like the corresponding chloride and bromide. - - -The Preparation of Cadmous Hydroxide and Oxide. - -When the substance Cd₄I₇ is treated with water a complicated reaction -takes place. The general character of the reaction appears to be the -same with the chloride, bromide and iodide. The decomposition of the -chloride was studied more thoroughly than that of the other compounds. - -When the finely powdered chloride is treated with water it yields -cadmic chloride which passes into solution, a small quantity of a white -flocculent material which may be cadmic hydroxide but which in no case -could be entirely freed from traces of chlorine, and a highly lustrous -crystalline substance which rapidly lost its crystalline appearance -and passed over into a grayish white amorphous compound, which when -freed from chlorine was found to be cadmous hydroxide, of the formula -Cd(OH). The separate products resulting from the treatment with water -were analyzed. - -First Analysis: - - Amount of Cd₄Cl₇ treated with water 1.45970 gr. - Cadmium found in flocculent precipitate .02318 ” - ” ” ” crystalline substance .09614 ” - ” ” ” solution in water .81970 ” - Total cadmium found .93902 ” - - Chlorine found in crystalline compound .00371 gr. - ” ” ” solution in water .51671 ” - Total chlorine found .52042 ” - -Approximately seven-eighths of the total cadmium dissolved as -cadmic chloride while the remainder was contained in the flocculent -precipitate and in the gray crystalline compound. - -Second Analysis: - - Amount of Cd₄Cl₇ treated with water 1.0794 gr. - Cadmium found in flocculent precipitate .01469 ” - ” ” ” solution in water .60795 ” - - Chlorine found in solution in water .38491 ” - -The percentage of cadmium in the white precipitate is less in this -analysis than in the former. The cadmium in solution is again about -seven-eighths of the total and the chlorine present in the same -solution shows that the cadmium was all combined as cadmic chloride. - -All attempts to determine the composition of the gray crystalline -compound failed, owing to the rapidity with which it decomposed with -water. Even with the most rapid work it could not be isolated in the -undecomposed condition. - -Analyses of the partially decomposed crystals gave variable proportions -of metal and halogen but never less than eight equivalents of the -former to one of the latter. - -While the decomposition of Cd₄Cl₇ with water cannot at present be fully -explained, yet it is clear from the analyses that one eighth of the -total cadmium is thrown down as a white precipitate and a crystalline -compound which as will be seen passes over into cadmous hydroxide. One -half of the cadmous chloride is oxidized to cadmic chloride taking the -chlorine from the other half. - -The compound Cd₄Cl₇ was treated directly with absolute alcohol with -the hope of obtaining the crystalline substance in an undecomposed -condition. Although a substance of the same general appearance as that -formed in the presence of water was obtained yet it decomposed so -readily that a satisfactory analysis could not be made. - -Notwithstanding the rapidity with which the decomposition of the -crystalline compound begins, long continued washing was necessary in -order to completely remove the chlorine. The extraction of the last -traces of the halogen is hastened by the use of warm instead of cold -water. The temperature of the water must not exceed 50°C. In water -whose temperature approaches the boiling point the hydroxide is slowly -decomposed with liberation of metal. - -The new hydroxide is a strong reducing agent. It dissolves in dilute -acids; yielding with nitric acid oxides of nitrogen, with hydrochloric -or sulphuric acid free hydrogen. After washing with warm water until -all the chlorine had disappeared, it was dried over phosphorus -pentoxide and analyzed. - -First determination of cadmium. - - Amount of substance used .0968 gr. - ” ” cadmium found .08415 ” - - Cadmium. - 86.93 per cent. - -Second determination of cadmium. - - Amount of substance used .09806 gr. - ” ” cadmium found .08522 ” - - Cadmium. - 86.91 per cent. - -The calculated percentage of cadmium in Cd(OH) is: - - Cadmium. - 86.79 per cent. - -The determination of water in cadmous hydroxide was made by placing a -small specimen tube containing the hydroxide in a Kjeldahl flask which -was heated in a bath of concentrated sulphuric acid. During the heating -a slow current of dry nitrogen was passed over the substance. - -First determination of water. - - Amount of substance used .08434 gr. - ” ” water found .00609 ” - - Water. 7.22 per cent. - -Second determination of water. - - Amount of substance used .08895 gr. - ” ” water found .00600 ” - - Water. 6.74 per cent. - -Third determination of water. - - Amount of substance used .11766 gr. - ” ” water found .00856 ” - - Water. 7.25 per cent. - - Average amount of water = 7.07 per cent. - -The calculated percentage of water in Cd(OH) is, 6.99. - -At the temperature at which concentrated sulphuric acid gives off -dense white fumes cadmous hydroxide gives off all its water and passes -over into a heavy yellow powder. At 150°C not a trace of water was -liberated. Under the microscope the yellow powder was found to consist -of minute translucent crystals. - -First determination of cadmium. - - Amount of substance used .08064 gr. - ” ” cadmium found .07511 ” - - Cadmium. 93.14 per cent. - -Second determination of cadmium. - - Amount of substance used .10846 gr. - ” ” cadmium found .10106 ” - - Cadmium. 93.17 per cent. - -The calculated percentage of metal in Cd₂O is 93.32 per cent. - -If water of too high temperature is employed in washing the -subhydroxide, the presence of free metal in it can be detected under -the microscope and by rubbing between agate surfaces. If the yellow -suboxide is strongly heated it breaks up into a mixture of oxide and -metal which possesses a distinctly green color. Towards acids the -suboxide conducts itself like the subhydroxide. - -It is a fact of some interest in connection with the periodic -arrangement of the elements, that the tendency toward the formation -of a lower series of compounds which becomes so strongly developed in -mercury begins to exhibit itself in some slight degree in cadmium. - - - - -Notes on Crystals of Metallic Cadmium. - - -The measurements of the cadmium crystals were made by Dr. Williams who -has very kindly furnished me with his results. - -No reliable crystallographic description of the element cadmium seems -thus far to have appeared--a fact due to the difficulty in obtaining -suitable material. The crystals examined, although not capable of -yielding entirely satisfactory results are nevertheless such as to make -them of interest. - -In 1852 G. Rose noted the fact that distilled cadmium collected at the -neck of the retort in drops which solidified as complex polyhedral -aggregates[13] similar to those formed by zinc[14]. In 1874 Kammerer -encountered the same aggregates which he explained as complicated -isometric combinations[15]. This opinion was cited in 1881 by -Rammelsberg[16]. In 1884 Brögger and Flink stated that in their opinion -zinc, magnesium and probably cadmium were from analogy with beryllium -which they had studied, hexagonal and holohedral.[17] - -[13] Pogg. Ann. 85, 293. - -[14] Amer. Chem. Journ. 11, 219. - -[15] Ber. d. deutch. Chem. Gesell. 1874, 1724. - -[16] Handb. d. krystallographisch physicalischen Chemie. I, 184. - -[17] Zeits & Kryst. 9, 236. - -This supposition has already been substantiated in the case of the two -former elements[18] while the present material leads to the same result -for the last named. - -The cadmium crystals were produced in the same manner as were those of -zinc and magnesium measured before, viz; by distillation in a vacuum. -The appearance of the tubes thus obtained was closely like that in the -other cases. - -[18] Amer. Chem. Journ. 11, 225 and Ibid. 12, 225. - -The polyhedral aggregates were abundant and reached considerable -dimensions. The crystallizing power of the cadmium however, seems to be -less, so that the only crystals suitable for measurement were extremely -minute. The largest individuals were barrel-shaped, like those of zinc -and resembled little piles of basal plates. Their side planes are not -infrequently uneven and bent, probably as the result of the softness -and great ductility of the metal. - -Only the most minute crystals show pyramidal planes of comparative -perfection. These are well suited for a microscopic examination, but -their small size renders their measurement on a reflecting goniometer -a matter of difficulty. After a careful search two crystals were -secured which, although they had a diameter of only one third of a -millimeter, from their microscopic appearances promised good results. -Their planes however were found to give compound reflections and a -somewhat disappointing variation in corresponding angles. On the best -crystal three zones were measured as follows: (normal angles) - - Zone I Zone II Zone III - 0001 : 01ī1 = 62° 35′ |0001 : 10ī1 = 62° 4′ |0001 : 1ī01 = 62° 29′ - 0001 : 01ī0 = 89° 50½′| | - 0001 : 01īī = 118° 57′ |0001 : 10īī = 118° 28′| - -The second crystal was much less satisfactory, since values for the -angle between the base and pyramid (0001): (01ī1) were obtained which -varied all the way from 61° 2′ to 63° 43′. These measurements must -therefore be regarded as of little or no value. If we average the -readings for this angle on the first crystal we obtain 62° 23′, from -which - - ̲a : ̲c = 1 : 1.6554. - -A comparison of the axial ratios of the four rhombohedral and four -holohedral hexagonal elements gives the following: - - - { Bismuth ̲a : ̲c = 1 : 1.3035 (G. Rose, 1849). - Rhombo- { Antimony ̲a : ̲c = 1 : 1.3235 (Laspeyres, 1875). - hedral. { Tellurium ̲a : ̲c = 1 : 1.3298 (G. Rose, 1849). - { Arsenic ̲a : ̲c = 1 : 1.4025 (Zepharovich, 1875). - - { Zinc ̲a : ̲c = 1 : 1.356425 (Williams and - { Burton, 1889). - Holohedral. { Beryllium ̲a : ̲c = 1 : 1.5802 (Brögger, 1884). - { Magnesium ̲a : ̲c = 1 : 1.6202 (Williams, 1890). - { Cadmium ̲a : ̲c = 1 : 1.6554 (Williams, 1891). - -Zinc appears from its axial ratio to belong rather to the rhombohedral -group and this is the only one of the last four elements upon which the -faintest indication of any divergence from a holohedral development -of all of its forms has been observed. On crystals of this substance -there is an occasional rhombohedral alternative of the faces of -certain of the pyramids, although the crystals otherwise appear to be -holohedral.[19] - -The crystals of cadmium like those of magnesium show only the three -forms OP (0001), P (10ī1)₂, and ∞P (10ī0). Brögger and Flink observed -on beryllium the additional forms ∞P₂ (2īī0) and ½P (20{̅2}1); while -upon zinc a large number of forms in the zone of the unit pyramid occur. - -[19] Amer. Chem. Journ. 11, 224. pl. 2 fig. 8. - -Not infrequently the cadmium crystals show a tendency toward a -hemimorphic development. This is plainly seen when a large number -of them are examined together under the microscope. The little -barrel-shaped crystals are mostly attached by their sides and yet one -of their ends is often broader than the other. Sometimes they taper -nearly to a point, quite like greenockite crystals. - - - - -The Cohesion Phenomena of Cadmium. - - -The cohesion phenomena of cadmium are similar to those of zinc but -are still more striking. When a crystal is sharply focused under the -microscope and then gently pressed on the side with the point of a -needle an unbroken pyramidal face is seen to suddenly become striated -parallel to the basal plane, as though a gliding in the basal section -took place. Some of these crystals were kindly examined by Prof. Otto -Mügge of Münster, Germany, who has added so much to our knowledge -of the cohesion phenomena in crystals. He has written in regard to -his observations as follows; “The cadmium crystals as far as their -gliding phenomena are concerned behave quite like zinc. If a crystal -is carefully loosened and then squeezed with a pair of pincers it is -easy to see that the smooth surface where it was attached to the glass -became striated parallel to OP (0001) and that at the same time two -other sets of striations are produced which meet at an angle of about -85° and intersect the trace of the basal plane at about 47½°. The plane -of attachment was selected for observation because it was smoother than -the pyramidal faces. In the above case this plane has the position of -a steep pyramid inclined to the base at an angle of about 100°. The -oblique sets of striations appear to represent gliding planes parallel -to the unit pyramid faces (2P (10ī2) of Rose) as in the case with zinc. -Whether the horizontal striations were due to gliding parallel to the -base I could not certainly decide. Many of the crystals appear when -pinched to be completely overturned, in which cases ordinary bending -accompanies gliding as in the case of gold set. This is shown by the -fact that both faces and striations become rounded.” - - - - -Biographical Sketch. - - -Harry Clary Jones was born near New London, Frederick County, Maryland, -Nov. 11ᵗʰ 1865. - -After attending several schools in that state he entered the Johns -Hopkins University in the autumn of 1885 as a special student of -chemistry and physics. He matriculated in 1887 and received the degree -of Bachelor of Arts in 1889, having held an ordinary and an honorary -scholarship. For the last three years he has continued his studies -in the University following chemistry as a principal subject and -mineralogy and geology as subordinates. During this time he has been -appointed twice to a university scholarship, was lecture assistant to -professor Remsen,90-91, and Fellow in chemistry,91-92. - -*** END OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC -WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS -SUB-COMPOUNDS *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. 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Jones—A Project Gutenberg eBook - </title> - <link rel="coverpage" href="images/cover.jpg" /> - <style type="text/css"> - -body { margin-left: 10%; margin-right: 10%; } - -h1,h2,h3,h4 { text-align: center; clear: both; } - -p { margin-top: .51em; text-align: justify; text-indent: 1.5em; margin-bottom: .49em; } -p.no-indent { margin-top: .51em; text-align: justify; text-indent: 0em; margin-bottom: .49em;} -p.indent { text-indent: 1.5em;} -p.neg-indent { text-indent: -1.5em; margin-left: 5%; margin-right: 5%; padding-left: 1.5em;} -p.f120 { font-size: 120%; text-align: center; text-indent: 0em; } -p.f150 { font-size: 150%; text-align: center; text-indent: 0em; } - -.fontsize_110 { font-size: 110%; } -.fontsize_120 { font-size: 120%; } - -.space-above1 { margin-top: 1em; } -.space-above2 { margin-top: 2em; } -.space-above3 { margin-top: 3em; } -.space-below1 { margin-bottom: 1em; } -.space-below2 { margin-bottom: 2em; } - -hr.chap {width: 65%; margin-left: 17.5%; margin-right: 17.5%; margin-top: 2em; margin-bottom: 2em;} - @media print { hr.chap {display: none; visibility: hidden;} } -hr.r5 {width: 5%; margin-top: 0.5em; margin-bottom: 0.5em; margin-left: 47.5%; margin-right: 47.5%;} -div.chapter {page-break-before: always;} -h2.nobreak {page-break-before: avoid;} -.no-wrap {white-space: nowrap; } - -ul.index { list-style-type: none; } -li.isub3 {text-indent: 3em;} -li.isub5 {text-indent: 5em;} - -table { margin-left: auto; margin-right: auto; } - -.tdl {text-align: left;} -.tdr {text-align: right;} -.tdc {text-align: center;} -.tdl_ws1 {text-align: left; vertical-align: top; padding-left: 1em;} -.tdl_ws2 {text-align: left; vertical-align: top; padding-left: 2em;} -.tdr_ws1 {text-align: right; vertical-align: top; padding-left: 1em;} - -.pagenum { - position: absolute; - left: 92%; - font-size: smaller; - text-align: right; - font-style: normal; - font-weight: normal; - font-variant: normal; -} - -.blockquot { margin-left: 10%; margin-right: 10%; } - -.bb {border-bottom: solid thin;} -.bt {border-top: solid thin;} -.br {border-right: solid thin;} -.bbox {border: solid medium;} - -.smcap {font-variant: small-caps;} -.u {text-decoration: underline;} -.over {text-decoration: overline;} - -img { max-width: 100%; height: auto; } - -.figcenter { margin: auto; text-align: center; - page-break-inside: avoid; max-width: 100%; } - -.footnotes {border: 1px dashed;} -.footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} -.footnote .label {position: absolute; right: 84%; text-align: right;} -.fnanchor { - vertical-align: super; - font-size: .8em; - text-decoration: - none; -} - -.transnote {background-color: #E6E6FA; - color: black; - font-size:smaller; - padding:0.5em; - margin-bottom:5em; - font-family:sans-serif, serif; } - -.ws2 {display: inline; margin-left: 0em; padding-left: 2em;} -.ws3 {display: inline; margin-left: 0em; padding-left: 3em;} - - </style> - </head> -<body> -<p style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Determination of The Atomic Weight Of Cadmium and The Preperation of Certain Of Its Sub-Compounds, by Harry C. Jones</p> -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online -at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Determination of The Atomic Weight Of Cadmium and The Preperation of Certain Of Its Sub-Compounds</p> -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Author: Harry C. Jones</p> -<p style='display:block; text-indent:0; margin:1em 0'>Release Date: February 13, 2022 [eBook #67396]</p> -<p style='display:block; text-indent:0; margin:1em 0'>Language: English</p> - <p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em; text-align:left'>Produced by: The Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)</p> -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS SUB-COMPOUNDS ***</div> - -<hr class="chap x-ebookmaker-drop" /> - -<h1>Determination of<br /> The Atomic Weight<br /> of Cadmium<br /> -and<br /> The Preparation of Certain<br /> Of Its Sub-Compounds.</h1> - -<p class="f150"><b>Dissertation,</b></p> - -<p class="f150">Presented to<br /> The Board of University Studies<br /> -of The Johns Hopkins University,</p> - -<p class="f150 space-above2">For The Degree of<br />Doctor of Philosophy,</p> - -<p class="f150">By<br />Harry C. Jones</p> - -<p class="f120">1892.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak u"><big><i>Contents.</i></big></h2> -</div> - -<table border="0" cellspacing="0" summary="TOC" cellpadding="2" > - <tbody><tr> - <td class="tdr" colspan="2">Page</td> - </tr><tr> - <td class="tdl fontsize_120">Determination of the Atomic Weight of Cadmium</td> - <td class="tdr"><a href="#Atomic_Weight"> 1</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Introduction and Historical Statement</td> - <td class="tdr"><a href="#Historical_1"> 2</a></td> - </tr><tr> - <td class="tdl fontsize_120">Preparation of Pure Cadmium</td> - <td class="tdr"><a href="#Prep_Cadmium">22</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Preparation of Pure Nitric Acid</td> - <td class="tdr"><a href="#Nitric">28</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Arrangement of Crucibles</td> - <td class="tdr"><a href="#Crucibles">30</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Mode of Procedure</td> - <td class="tdr"><a href="#Mode_1">32</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Weighing</td> - <td class="tdr"><a href="#Weigh_1">37</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Taring the Crucibles</td> - <td class="tdr"><a href="#Tare">40</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Results</td> - <td class="tdr"><a href="#Results_1">42</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Objections to the Method</td> - <td class="tdr"><a href="#Objections_1">45</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Advantages of the Method</td> - <td class="tdr"><a href="#Advantages_1">48</a></td> - </tr><tr> - <td class="tdl fontsize_120">The Oxalate Method</td> - <td class="tdr"><a href="#Oxalate">50</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Preparation of Pure Oxalic Acid</td> - <td class="tdr"><a href="#Oxalic">51</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Preparation of Cadmium Oxalate</td> - <td class="tdr"><a href="#Prep_Oxalate">52</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Mode of Procedure</td> - <td class="tdr"><a href="#Mode_2">53</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Drying and Weighing of the Oxalate</td> - <td class="tdr"><a href="#Weigh_2">55</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Results</td> - <td class="tdr"><a href="#Results_2">58</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Advantages of the Method</td> - <td class="tdr"><a href="#Advantages_2">60</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Disadvantages of the Method</td> - <td class="tdr"><a href="#Disadvantages">61</a></td> - </tr><tr> - <td class="tdl fontsize_120">Preparation of Certain Sub-compounds of Cadmium  </td> - <td class="tdr"><a href="#Sub-compounds">63</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">Historical</td> - <td class="tdr"><a href="#Historical_2">64</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Preparation of Cd₄Cl₇</td> - <td class="tdr"><a href="#Prep_Chloride">66</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Preparation of Cd₄Br₇</td> - <td class="tdr"><a href="#Prep_Bromide">78</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Preparation of Cd₁₂I₂₃</td> - <td class="tdr"><a href="#Prep_Iodide">82</a></td> - </tr><tr> - <td class="tdl_ws2 fontsize_110">The Preparation of Cadmium Hydroxide and Oxide</td> - <td class="tdr"><a href="#Prep_Oxide">82</a></td> - </tr><tr> - <td class="tdl fontsize_120">Notes on Crystals of Metallic Cadmium</td> - <td class="tdr"><a href="#Notes">97</a></td> - </tr><tr> - <td class="tdl fontsize_120">The Cohesion Phenomena of Cadmium</td> - <td class="tdr"><a href="#Cohesion">103</a></td> - </tr><tr> - <td class="tdl fontsize_120">Biographical Sketch</td> - <td class="tdr"><a href="#Biographical">106</a></td> - </tr> - </tbody> -</table> - -<hr class="chap x-ebookmaker-drop" /> -<div class="chapter"> -<p class="f150"><b>Acknowledgment.</b></p> -</div> - -<p class="blockquot">It affords me great pleasure to express my sincere -thanks to Professor Remsen for his instruction and personal supervision -during my entire connection with the University; to Dr. Morse, under -whose immediate guidance the work described in this dissertation -was completed; to Dr. Renouf for valuable assistance in qualitative -chemistry and to Dr. Williams, with whom the branches of mineralogy and -geology were followed as subordinate subjects.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_1">[Pg 1]</span></p> -<h2 class="nobreak" id="Atomic_Weight">Determination of the<br /> -Atomic Weight of Cadmium.</h2> -</div> -<p><span class="pagenum" id="Page_2">[Pg 2]</span></p> - -<h3 id="Historical_1">Introduction and Historical statement.</h3> - -<p>A careful examination of the literature on the atomic weight of cadmium -will convince any one that considerable uncertainty yet remains in -reference to this constant. Six experimenters have worked on this -problem but the results of no one of them can be accepted as being more -accurate than those of all others. The value assigned to cadmium varies -from 111.48 to 112.32 on the basis of oxygen = 16. The best work has -apparently been done by von Hauer, Lenssen and Huntington. The results -of these three seem entitled to about equal confidence, yet the figure -obtained by von Hauer differs from that of Huntington by three tenths -of a unit. -<span class="pagenum" id="Page_3">[Pg 3]</span></p> - -<p>The more prominent difficulties which have been encountered were:</p> - -<div class="blockquot"> -<p class="no-indent">First. The preparation of cadmium compounds free from all -impurities, and which at the same time were well adapted to weighing.</p> - -<p class="no-indent">Second. The lack of a thoroughly simple and exact method for the -analysis of cadmium compounds.</p> - -<p class="no-indent">Third. Insufficient care in weighing in many cases whereby small -errors were introduced into the results.</p> -</div> - -<p>The methods which have been employed are:</p> - -<div class="blockquot"> -<p class="neg-indent">1 Conversion of the metal into the oxide. -(Stromeyer).</p> - -<p class="neg-indent">2 Conversion of the sulphate into the sulphide. -(von Hauer and Partridge).</p> - -<p class="neg-indent">3 Decomposition of the oxalate to the oxide. -(Lenssen and Partridge).</p> - -<p class="neg-indent">4 Determination of the chlorine in cadmium -chloride, by which the relation between the chloride and metallic -silver was established. (Dumas.)</p> - -<p class="neg-indent">5 Precipitation of the bromine in cadmium bromide -as silver bromide. (Huntington.)</p> - -<p class="neg-indent">6 The conversion of the oxalate into the -sulphide. (Partridge.)</p> -</div> - -<p>The different pieces of work will be taken up in chronological order -and briefly considered.</p> - -<p>Stromeyer, Schurigg Journ. 22, 366. 1818, determined the atomic weight -of cadmium a short time after the discovery of the element. He does -not describe his method in detail but established the relation between -cadmium and oxygen to be:</p> - -<p class="f120">Cd : O = 100 : 14.352.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">If the atomic weight of</td> - <td class="tdr_ws1">oxygen =</td> - <td class="tdr">16,<span class="ws2"> </span></td> - </tr><tr> - <td class="tdl">  ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">cadmium =</td> - <td class="tdr">111.483.</td> - </tr> - </tbody> -</table> - -<p>The very low result as compared with all subsequent work was probably -due to the presence of a small amount of zinc, since the cadmium used -was obtained from zinc ores and no adequate means of separation from -the zinc is described.</p> - -<p>von Hauer, Journ. f. prakt. Chem. 72, 338. 1857. His method consisted -in reducing a weighed amount of cadmium sulphate to the sulphide -in a stream of hydrogen sulphide, under pressure, at an elevated -temperature, and weighing the sulphide. The reduction was shown to be -complete by proving the absence of sulphate in the sulphide.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl"> </td> - <td class="tdl_ws1">64.2051</td> - <td class="tdl_ws1">grams of</td> - <td class="tdl_ws1">cadmium sulphate</td> - </tr><tr> - <td class="tdl">gave</td> - <td class="tdl_ws1">44.4491</td> - <td class="tdl_ws1"> ”  ”</td> - <td class="tdl_ws1"><span class="ws2"> </span>”  sulphide.</td> - </tr> - </tbody> -</table> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">If the atomic weight of</td> - <td class="tdr_ws1">oxygen =</td> - <td class="tdr">16,   </td> - </tr><tr> - <td class="tdl">”  ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">sulphur =</td> - <td class="tdr">32.059,</td> - </tr><tr> - <td class="tdl">  ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">cadmium =</td> - <td class="tdr">111.935.</td> - </tr> - </tbody> -</table> - -<p>The atomic weight of cadmium calculated as an average of the nine -determinations made using the above values for oxygen and sulphur = 111.94.</p> - -<ul class="index fontsize_110"> -<li class="isub3"> Maximum, 112.121.</li> -<li class="isub3"> Minimum, 111.796.</li> -<li class="isub5">Mean, 111.940.</li> -</ul> - -<p>The work of von Hauer is greatly to be preferred to that of Stromeyer. -The large amount of material used in each determination tended to -lessen any experimental error. A very considerable degree of care -seems to have been exercised in purifying the cadmium sulphate. In -determinations 1-5 a different specimen of sulphate was employed from -<span class="pagenum" id="Page_7">[Pg 7]</span> -that in determinations 6-9. The average value found in the first -five determinations = 111.910, in the last four = 111.977. The close -agreement between the results obtained from the different preparations of -the sulphate argues in favor of a fair degree of purity for all the material.</p> - -<p>The method of weighing the more or less hygroscopic cadmium sulphate is -open to criticism when employed in accurate work. The cadmium sulphate -was placed in an open boat, dried, cooled over sulphuric acid, and -weighed. It was again dried, cooled as before, and weighed. The second -weighing could be quickly accomplished since the approximate weight was -known. The two weighings agreed to within less than a milligram or a -<span class="pagenum" id="Page_8">[Pg 8]</span> -third drying and weighing were made. An error of a milligram in -the weight of the sulphate produced an average error in the atomic -weight of cadmium of about .06. That a discrepancy of greater or less -magnitude was introduced from this source will be readily seen.</p> - -<p>Dumas Ann. Chim. Phys. 55, 158. 1859, determined the relation between -cadmium chloride and the metallic silver required to precipitate the -chlorine. Metallic cadmium was dissolved in boiling hydrochloric acid -and the solution evaporated. The cadmium chloride was fused for five or -six hours in a stream of hydrochloric acid gas. Six determinations were -made. 23.0645 grams of cadmium chloride were equivalent to 27.173 grams -of metallic silver. -<span class="pagenum" id="Page_9">[Pg 9]</span></p> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">If the atomic weight of</td> - <td class="tdr_ws1">silver =</td> - <td class="tdr">107.93. </td> - </tr><tr> - <td class="tdl">”  ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">chlorine =</td> - <td class="tdr">35.45. </td> - </tr><tr> - <td class="tdl">   ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">cadmium =</td> - <td class="tdr">112.322.</td> - </tr> - </tbody> -</table> - -<p>The atomic weight of cadmium calculated as the average of the six -determinations made, using the above values for silver and chlorine = 112.241.</p> - -<ul class="index fontsize_110"> -<li class="isub3"> Maximum, 112.759.</li> -<li class="isub3"> Minimum, 111.756.</li> -<li class="isub5">Mean, 112.241.</li> -</ul> - -<p>The large difference between the results would indicate some -considerable source of error in part or all of the determinations. -The first three determinations were made from a different specimen -of cadmium from the last three.</p> - -<p>In the first three the cadmium used does not seem to have been purified -<span class="pagenum" id="Page_10">[Pg 10]</span> -and the cadmium chloride prepared from it was more or less tinted -brown. In the last three a new specimen of metal was used which in -Dumas’ words could reasonably be considered to be absolutely pure. -The chloride prepared from it was colorless, well crystallized -and perfectly soluble in water. In order to show clearly the wide -discrepancy between the results obtained from the two specimens of -cadmium which were used, the separate determinations are given in detail.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdr" colspan="4">At. Wt. </th> - </tr><tr> - <th class="tdc bb"> </th> - <th class="tdc bb">CdCl₂</th> - <th class="tdc bb">Ag.</th> - <th class="tdc bb">Cadmium.</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc"> 1 </td> - <td class="tdl_ws1">2.369</td> - <td class="tdl_ws1">2.791</td> - <td class="tdl_ws1">112.322</td> - </tr><tr> - <td class="tdc">2</td> - <td class="tdl_ws1">4.540</td> - <td class="tdl_ws1">5.348</td> - <td class="tdl_ws1">112.347</td> - </tr><tr> - <td class="tdc">3</td> - <td class="tdl_ws1">6.177</td> - <td class="tdl_ws1">7.260</td> - <td class="tdl_ws1">112.759</td> - </tr><tr> - <td class="tdc">4</td> - <td class="tdl_ws1">2.404</td> - <td class="tdl_ws1">2.841</td> - <td class="tdl_ws1">111.756</td> - </tr><tr> - <td class="tdc">5</td> - <td class="tdl_ws1">3.5325</td> - <td class="tdl_ws1">4.166</td> - <td class="tdl_ws1">112.135</td> - </tr><tr> - <td class="tdc">6</td> - <td class="tdl_ws1">4.042</td> - <td class="tdl_ws1">4.767</td> - <td class="tdl_ws1">112.130</td> - </tr> - </tbody> -</table> - -<p class="space-above1">The average result of the first three determinations = 112.476. -The average result of the last three determinations = 112.007. From Dumas’ -own statement concerning the purity of the cadmium chloride analyzed, -determinations 4-6 are much to be preferred to determinations 1-3 and -the most probable value from Dumas’ work would be very nearly 112.</p> - -<p>Lenssen Journ. f. prakt. Chem. 79, 281. 1860, regarded the oxalate of -cadmium as well adapted to the determination of the atomic weight of -cadmium. A solution of cadmium chloride which had been purified by -repeated crystallization was treated with an excess of a solution of -pure oxalic acid. The cadmium oxalate formed was filtered off, washed, -and carefully dried in the air at 150° C. until the last trace of water -<span class="pagenum" id="Page_12">[Pg 12]</span> -was removed. 1.5697 grams cadmium oxalate gave 1.0047 grams cadmium oxide.</p> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">If the atomic weight of</td> - <td class="tdr_ws1">oxygen =</td> - <td class="tdr">16,   </td> - </tr><tr> - <td class="tdl">”  ” <span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">carbon =</td> - <td class="tdr">12.003,</td> - </tr><tr> - <td class="tdl">  ” <span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">cadmium =</td> - <td class="tdr">112.043.</td> - </tr> - </tbody> -</table> - -<p>The average of the three determinations using the above values for -oxygen and carbon is 112.067.</p> - -<ul class="index fontsize_110"> -<li class="isub3"> Maximum, 112.304.</li> -<li class="isub3"> Minimum, 111.911.</li> -<li class="isub5">Mean, 112.067.</li> -</ul> - -<p>The small amount of material used in each determination, the small -number of determinations made, and the rather large difference between -the highest and lowest result are objectionable. There are certain weak -points in the method but to these reference will be made later. -<span class="pagenum" id="Page_13">[Pg 13]</span></p> - -<p>Huntington, Proc. Amer. Acad. 17, 28. 1882, working with Cooke, made -two series of determinations of the atomic weight of cadmium. In the -first series the relation between cadmium bromide and the silver -bromide formed from it was determined. In the second, the relation -between cadmium bromide and the silver required to precipitate the bromine.</p> - -<p>The cadmium bromide was prepared by dissolving the carbonate in -hydrobromic acid and subliming the product in a stream of carbon dioxide.</p> - -<p>In the first series of eight determinations 23.3275 grams of cadmium -bromide were equivalent to 32.2098 grams of silver bromide.</p> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">If the atomic weight of</td> - <td class="tdr_ws1">silver =</td> - <td class="tdr">107.93. </td> - </tr><tr> - <td class="tdl">”  ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">bromine =</td> - <td class="tdr">79.95. </td> - </tr><tr> - <td class="tdl">   ” ”<span class="ws3">”</span><span class="ws2">”</span></td> - <td class="tdr_ws1">cadmium =</td> - <td class="tdr">122.239. - <span class="pagenum" id="Page_14">[Pg 14]</span></td> - </tr> - </tbody> -</table> - -<ul class="index fontsize_110"> -<li class="isub3"> Maximum, 112.290.</li> -<li class="isub3"> Minimum, 112.169.</li> -</ul> - -<p>Where the difference between the maximum and minimum value is slight, -the average of the separate determinations agrees closely with the -number found by comparing the total substance used with the total product -obtained. The latter method of calculation seems however to be preferable.</p> - -<p>In the second series of eight determinations 28.6668 grams of cadmium -bromide were equivalent to 22.7379 grams of silver.</p> - -<p>Using the same values for silver and bromine, the atomic weight of -cadmium = 112.245.</p> - -<ul class="index fontsize_110"> -<li class="isub3"> Maximum, 112.320.</li> -<li class="isub3"> Minimum, 112.180.</li> -</ul> - -<p>The agreement of the separate determinations with each other is fairly -<span class="pagenum" id="Page_15">[Pg 15]</span> -close and the average of the two series of determinations is nearly the -same. Huntington took great care in the purification of his material -and in the carrying out of his method, which are strong arguments in -favor of his work, yet his method is not as simple as could be desired -where the nature of the work demands the greatest possible accuracy in -all details and it also appears to be subject to some of the errors -common to ordinary analytical operations.</p> - -<p>Partridge. Amer. Journ. Science XL, 377. 1890. Methods: 1ˢᵗ. -Decomposition of the oxalate to the oxide. 2ⁿᵈ. Reduction of the -sulphate to the sulphide. 3ʳᵈ. Conversion of the oxalate into the -sulphide. As an average of the determinations made by each method -Partridge gives: -<span class="pagenum" id="Page_16">[Pg 16]</span></p> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl">1ˢᵗ series,</td> - <td class="tdl">atomic weight of cadmium</td> - <td class="tdr">= 111.8027.</td> - </tr><tr> - <td class="tdl">2ⁿᵈ ”</td> - <td class="tdl_ws1">”<span class="ws3">”</span> ”<span class="ws2">”</span></td> - <td class="tdr">= 111.7969.</td> - </tr><tr> - <td class="tdl">3ʳᵈ ”</td> - <td class="tdl_ws1">”<span class="ws3">”</span> ”<span class="ws2">”</span></td> - <td class="tdr">= 111.8050.</td> - </tr> - </tbody> -</table> - -<p>An excellent agreement between results obtained by different -methods<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">[1]</a>.</p> - -<p>That this very close agreement is only apparent has been shown by -Clarke. He has found that the above calculations are based on the -assumption that the atomic weight of carbon = 12, and that of sulphur -= 32 when oxygen = 16. There seems to be little justification for -this rather arbitrary selection by Partridge since the most refined -work shows that whole numbers do not express the most probable atomic -weights of carbon and sulphur in a system where oxygen = 16.</p> - -<p>The atomic weight of cadmium calculated from the total material used -and the total product found in each of the three series is:</p> - -<table class="space-above1 fontsize_110 no-wrap" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc"> </th> - <th class="tdc">O = 16.</th> - <th class="tdc">C = 12.</th> - <th class="tdc">S = 32.</th> - <th class="tdc"> At.Wt.Cd.</th> - </tr> - </thead> - <tbody><tr> - <td class="tdl">1ˢᵗ series, </td> - <td class="tdc">CdC₂O₄ : CdO =</td> - <td class="tdc">12.66368g. :</td> - <td class="tdc"> 8.10031g.</td> - <td class="tdr">111.805.</td> - </tr><tr> - <td class="tdl">2ⁿᵈ ”</td> - <td class="tdc">CdSO₄ : CdS =</td> - <td class="tdc">15.93505g. :</td> - <td class="tdc">11.02691g.</td> - <td class="tdr">111.786.</td> - </tr><tr> - <td class="tdl">3ʳᵈ ”</td> - <td class="tdc">CdC₂O₄ : CdS =</td> - <td class="tdc">16.85228g. :</td> - <td class="tdc">12.12906g.</td> - <td class="tdr">111.806.</td> - </tr><tr> - <td class="tdr" colspan="4">difference, </td> - <td class="tdr">0.020.</td> - </tr> - </tbody> -</table> -<table class="no-wrap space-above1 fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc"> </th> - <th class="tdc">O = 16.</th> - <th class="tdc">C = 12.003</th> - <th class="tdc">S = 32.059</th> - <th class="tdc"> At.Wt.Cd.</th> - </tr> - </thead> - <tbody><tr> - <td class="tdl">1ˢᵗ series, </td> - <td class="tdc">CdC₂O₄ : CdO =</td> - <td class="tdc">12.66368g. :</td> - <td class="tdc"> 8.10031g.</td> - <td class="tdr">111.816.</td> - </tr><tr> - <td class="tdl">2ⁿᵈ ”</td> - <td class="tdc">CdSO₄ : CdS =</td> - <td class="tdc">15.93505g. :</td> - <td class="tdc">11.02691g.</td> - <td class="tdr">111.727.</td> - </tr><tr> - <td class="tdl">3ʳᵈ ”</td> - <td class="tdc">CdC₂O₄ : CdS =</td> - <td class="tdc">16.85228g. :</td> - <td class="tdc">12.12906g.</td> - <td class="tdr">111.610.</td> - </tr><tr> - <td class="tdr" colspan="4">difference, </td> - <td class="tdr">0.206.</td> - </tr> - </tbody> -</table> - -<p>As Clarke has pointed out when those values are chosen for carbon -and sulphur which are founded on the best experimental evidence the -agreement between the different series of results as calculated by -Partridge is somewhat modified.</p> - -<p>I have repeated the work on which series I is based and would call -attention to the following points in which it appears to have been -experimentally defective.</p> - -<div class="blockquot"> -<p class="neg-indent">1 The metal was only distilled twice in a vacuum. -It has been found in this laboratory that perfectly pure cadmium or -zinc can be prepared only by repeated distillations, each one being -carried on slowly to allow the impurities to separate by means of their -difference in volatility.</p> - -<p class="neg-indent">2 The supposed mixture of metal and oxide -resulting from the decomposition of the oxalate was only moistened with -a few drops of nitric acid in order to reoxidize any reduced metal. -<span class="pagenum" id="Page_19">[Pg 19]</span> -Unless the entire mass of metal and oxide was dissolved there would be -danger of the presence of free undissolved metal which would possess -an appreciable vapor-tension below the temperature of decomposition -of cadmium nitrate. An appreciable loss in weight resulting from a -distillation of the metal out of the crucible might easily result.</p> - -<p class="neg-indent">3 It seems very probable that the cadmium nitrate -was not heated sufficiently to remove all traces of the oxides of -nitrogen. I have found that this could only be accomplished by long -continued heating. Constant weight was not sufficient to have decided -this point since it was also found that this could be reached short of -complete decomposition, if the temperature was too low to remove the -last traces of these oxides. Some very delicate test for such oxides -should have been applied at the end of each experiment.</p> -</div> - -<p>The following table contains a summary of the results thus far obtained.</p> - -<p>When two values are given for one series of determinations, the first -is calculated from the total material used and the total product found, -the second is an average of the results of the separate experiments. -Oxygen is taken as 16 throughout.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc bb">Date.</th> - <th class="tdl bb" colspan="2">Investigators.</th> - <th class="tdr bb">At.Wt.Cd.</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc">1818,</td> - <td class="tdl_ws1" colspan="2">Stromeyer,</td> - <td class="tdl_ws1">111.483</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">1857,</td> - <td class="tdl_ws1" colspan="2">von Hauer,</td> - <td class="tdl_ws1">111.935</td> - <td class="tdc" rowspan="2"><img src="images/cbr-2.jpg" alt="" width="9" height="32" /></td> - </tr><tr> - <td class="tdc" colspan="3"> </td> - <td class="tdl_ws1">111.940</td> - </tr><tr> - <td class="tdc">1859,</td> - <td class="tdl_ws1" colspan="2">Dumas,</td> - <td class="tdl_ws1">112.322</td> - <td class="tdc" rowspan="2"><img src="images/cbr-2.jpg" alt="" width="9" height="32" /></td> - </tr><tr> - <td class="tdc" colspan="3"> </td> - <td class="tdl_ws1">112.241</td> - </tr><tr> - <td class="tdc">1860,</td> - <td class="tdl_ws1" colspan="2">Lenssen,</td> - <td class="tdl_ws1">112.043</td> - <td class="tdc" rowspan="2"><img src="images/cbr-2.jpg" alt="" width="9" height="32" /></td> - </tr><tr> - <td class="tdc" colspan="3"> </td> - <td class="tdl_ws1">112.067</td> - </tr><tr> - <td class="tdc">1882,</td> - <td class="tdl_ws1">Huntington,</td> - <td class="tdl_ws1">1ˢᵗ series</td> - <td class="tdl_ws1">112.239</td> - <td class="tdc"> - <span class="pagenum" id="Page_21">[Pg 21]</span></td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">”</td> - <td class="tdl_ws1">2ⁿᵈ ”</td> - <td class="tdl_ws1">112.245</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">1890,</td> - <td class="tdl_ws1">Partridge,</td> - <td class="tdl_ws1">1ˢᵗ series</td> - <td class="tdl_ws1">111.805</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">”</td> - <td class="tdl_ws1">2ⁿᵈ ”</td> - <td class="tdl_ws1">111.786</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">”</td> - <td class="tdl_ws1">3ʳᵈ ”</td> - <td class="tdl_ws1">111.806</td> - <td class="tdc"> </td> - </tr> - </tbody> -</table> - -<p class="blockquot">In the above calculation of Partridge’s results C = 12. S = 32. -In the following carbon is taken as 12.003 and sulphur is 32.059.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">1890,</td> - <td class="tdl_ws1">Partridge,</td> - <td class="tdl_ws1">1ˢᵗ series</td> - <td class="tdl_ws1">111.816</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">”</td> - <td class="tdl_ws1">2ⁿᵈ ”</td> - <td class="tdl_ws1">111.727</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">”</td> - <td class="tdl_ws1">3ʳᵈ ”</td> - <td class="tdl_ws1">111.610</td> - <td class="tdc"> </td> - </tr> - </tbody> -</table> - -<p>After a careful examination of the methods available it becomes evident -that no one of them was <i>per se</i> as accurate as the method -employed by Morse and Burton,<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">[2]</a> -for the determination of the atomic weight of zinc, and more recently by Burton and -Morse,<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">[3]</a> for the -<span class="pagenum" id="Page_22">[Pg 22]</span> -determination of the atomic weight of magnesium. The method of work -was to prepare pure metallic cadmium, to convert a weighed portion of -the metal into nitrate by means of pure nitric acid, to decompose the -nitrate completely to oxide and to weigh the oxide.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="Prep_Cadmium">Preparation of Pure Cadmium.</h2> -</div> - -<p>The work of preparing pure cadmium was begun more than two years ago -by Mr. W. V. Metcalf with Dr. H. N. Morse. I wish to express here -my sincere thanks to him for the material with which the following -determinations were made. The cadmium used by him was obtained from -Schuchart and marked “Met. prss. (galv.) redus.” -<span class="pagenum" id="Page_23">[Pg 23]</span></p> - -<p>The method of purification by fractional distillation in a vacuum, was -essentially that employed by Morse and Burton for the purification of -metallic zinc.</p> - -<p class="space-below2">The distillation was carried out in hard glass -tubes of the size of ordinary combustion tubing.</p> - -<div id="FIG_1" class="figcenter"> - <p class="f120"><b><span class="smcap">Fig. 1.</span></b></p> - <img src="images/fig01.jpg" alt="" width="600" height="162" /> -</div> - -<p><a href="#FIG_1">Fig. 1.</a> represents such a tube. A hard glass tube, -600-700 mm. in length, was closed at one end and about 130 grams of cadmium -introduced. The walls of the tube were heated and indented at the two -points a, and b, with a red-hot file, dividing the tube into three -sections marked A, B and C. The open end of the tube was drawn out, -bent, and attached to a Sprengel air-pump by means of a rubber tube. -<span class="pagenum" id="Page_24">[Pg 24]</span></p> - -<p>The joint was tied tightly with waxed cord and surrounded by mercury. -When the manometer indicated that the tube was exhausted, it was -gradually heated by the combustion furnace in which it rested. The -metal in A melted and distilled slowly into the front portion of the -tube. Most of it condensed in B, while a small part, together with any -more volatile impurity, collected in C which was kept cooler than the -remainder of the tube. When about four-fifths of the metal placed in -A had distilled over, the tube was very slowly cooled. When cold, the -tube was broken open, the portions in A and C being rejected in every -case, while the metal was recovered from B in the form of a bar resting -<span class="pagenum" id="Page_25">[Pg 25]</span> -on the bottom of the tube, together with some crystal aggregates, -suspended from the top and sides. A few crystal individuals were -secured but the measurement of these will be considered later. The -metal separated from the glass with a highly lustrous surface and did -not attack the glass in the least.</p> - -<p>The first distillation was effected in a tube bridged as represented -in <a href="#FIG_1">Fig. 1</a>, but drawn out at each end. The original cadmium -powder was heated in the tube in a stream of pure hydrogen gas, for the purpose -of obtaining the metal in the form of bars, and to reduce any cadmium -oxide contained in the powder.</p> - -<p>Six distillations were made in a vacuum. In the first, 630 grams of -metal were used being distilled in quantities of about 130 grams each. -<span class="pagenum" id="Page_26">[Pg 26]</span> -At the end of the sixth distillation, there were about 100 grams of -pure cadmium at disposal. In the fifth and sixth distillations, the -metal was heated just above the melting point for from twenty to -twenty-four hours, before being forced over into the middle portion of -the tube. By this means all the remaining traces of the more volatile -arsenic were driven into the front part of the tube and separated from -the cadmium.</p> - -<p class="f120"><b>The distillations.</b></p> - -<p>The residue represents the undistilled portion remaining in A. The -distillate, the material obtained from B after the distillation was -completed. The coating, the substance which condensed in C.</p> - -<table class="space-above1 fontsize_110" border="0" cellspacing="0" - summary="Distillations" cellpadding="2" > - <tbody><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd, Pt, Zn,? As?.</td> - </tr><tr> - <td class="tdl">Distillation I</td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd,   Zn,? As?</td> - </tr><tr> - <td class="tdl bb"> </td> - <td class="tdr bb">Coating,</td> - <td class="tdl_ws1 bb">Cd,   Zn,? As?. - <span class="pagenum" id="Page_27">[Pg 27]</span></td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl">Distillation II</td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl bb"> </td> - <td class="tdr bb">Coating,</td> - <td class="tdl_ws1 bb">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl">Distillation III </td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl bb"> </td> - <td class="tdr bb">Coating,</td> - <td class="tdl_ws1 bb">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl">Distillation IV</td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl bb"> </td> - <td class="tdr bb">Coating,</td> - <td class="tdl_ws1 bb">Cd, Zn?, As?.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd.</td> - </tr><tr> - <td class="tdl">Distillation V</td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd.</td> - </tr><tr> - <td class="tdl bb"> </td> - <td class="tdr bb">Coating,</td> - <td class="tdl_ws1 bb">Cd, As?.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Residue,</td> - <td class="tdl_ws1">Cd.</td> - </tr><tr> - <td class="tdl">Distillation VI</td> - <td class="tdr">Distillate,</td> - <td class="tdl_ws1">Cd.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdr">Coating,</td> - <td class="tdl_ws1">Cd.</td> - </tr> - </tbody> -</table> - -<p class="space-above2"><span class="pagenum" id="Page_28">[Pg 28]</span> -The distillate from the last distillation was examined -spectroscopically by Professor Rowland and found to be free from all -traces of impurity which would be detected by that method. The chemical -test for arsenic was more delicate than the spectroscopic and this -failed to reveal a trace.</p> - -<h3 id="Nitric">The preparation of pure nitric acid.</h3> - -<p>The method of preparing the pure acid and of preserving and transferring -it was the same as adopted by Morse and Burton in their work on the -atomic weight of zinc.</p> - -<div id="FIG_2" class="figcenter"> - <p class="f120 space-above2"><b><span class="smcap">Fig. 2.</span></b></p> - <img src="images/fig02.jpg" alt="" width="600" height="276" /> -</div> - -<p><span class="pagenum" id="Page_29">[Pg 29]</span> -The simple form of apparatus is represented in <a href="#FIG_2">fig. 2</a>. A large -platinum vessel containing fragments of ice was supported on a smaller platinum -dish, from which it was separated by hooks of large platinum wire. The -acid was distilled from a small flask as represented in the drawing.</p> - -<p class="space-below2">The purest nitric acid which could be obtained -was diluted with about an equal volume of water. The vessel containing -the acid was heated very gently that the distillation might take place -without boiling. The dilute acid condensed on the cold surface of the -larger dish and collected in the smaller, in which it was preserved -until used. This acid gave no residue on evaporation. -<span class="pagenum" id="Page_30">[Pg 30]</span></p> - -<h3 id="Crucibles">The arrangement of crucibles.</h3> - -<div id="FIG_3" class="figcenter"> - <p class="f120 space-above2"><b><span class="smcap">Fig. 3.</span></b></p> - <img src="images/fig03.jpg" alt="" width="600" height="307" /> -</div> - -<p>The arrangement of the crucibles in which the determinations were -made is represented in <a href="#FIG_3">fig. 3</a>. 1 is a small porcelain crucible, -(00) from the exterior and lid of which the glaze had been removed by -hydrofluoric acid. The lid was separated from the crucible by hooks -made from thick platinum wire, to allow free communication between the -contents of the crucible and the external air. This would facilitate -<span class="pagenum" id="Page_31">[Pg 31]</span> -the outward diffusion of the oxides of nitrogen when liberated from -the nitrate. 2 is an uncovered porcelain crucible (no. II) in which 1 -was placed. From the exterior the glaze had been removed to prevent -the crucible from adhering to the unglazed porcelain scorifier on -which it rested. The exterior was carefully brushed after treatment -with hydrofluoric acid to remove all loose particles adhering to its -surface. Crucibles 1 and 2 were not separated during a determination.</p> - -<p>3 is a nickel crucible about two and a half inches in diameter. The -porcelain crucibles were not allowed to touch the nickel at any point. -The nickel crucible was covered by a lid of nickel. -<span class="pagenum" id="Page_32">[Pg 32]</span></p> - -<h3 id="Mode_1">The mode of procedure.</h3> - -<p>A piece of cadmium weighing from two to three grams was cut from the -bar of the metal by means of a steel chisel. This was seized with steel -forceps and filed with a hard steel file to about one half the original -weight. Care was taken to remove the entire exterior portion of the -metal which had come in contact with the chisel or had stood exposed to -the air. The plug of metal was then carefully brushed and examined with -a lens to insure the removal of all loose particles from the surface.</p> - -<p><a href="#FIG_3">Crucibles 1 and 2</a> having been brought to constant weight -against their tare, were ready for use. The piece of cadmium was weighed and placed -in 1. An excess of pure nitric acid was added and a gentle heat applied -<span class="pagenum" id="Page_33">[Pg 33]</span> -until all the metal had dissolved. This required from twenty to forty hours.</p> - -<p>A sand-bath was constructed by placing a large porcelain crucible in -an iron crucible and filling the intervening space with sand. The pair -of crucibles (<a href="#FIG_3">1 and 2</a>) was placed in the porcelain crucible -and the contents evaporated to dryness by warming very carefully at first and -gradually increasing the temperature. The pair of crucibles was then -transferred to a bath constructed as the above where iron filings -took the place of sand. This was heated by a single burner until the -nitrate was all decomposed when a triple burner was added and finally -two for six or eight hours. This was not sufficient to effect complete -<span class="pagenum" id="Page_34">[Pg 34]</span> -decomposition. When cold, the pair of crucibles was placed in the -nickel crucible as represented in <a href="#FIG_3">fig. 3</a> and sharply heated -over a blast-lamp for several hours. This completed the decomposition of the -nitrate and the removal of the last traces of oxides of nitrogen.</p> - -<p>During the blasting the lid on crucible 3 was raised a little to one -side to allow free access of air. The nickel crucible was forced -tightly into a hole cut in the center of an asbestos board about -ten inches in diameter, to prevent any reducing gases from the lamp -entering the crucibles while hot. This was the same arrangement as was -used by Partridge<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">[4]</a>.</p> - -<p>It was found that the final decomposition of the nitrate could not -be effected in a muffle furnace as with zinc, since at very high -<span class="pagenum" id="Page_35">[Pg 35]</span> -temperatures cadmium oxide attacked the porcelain with great energy and -injured the crucibles.</p> - -<p>The decomposition of the nitrate was shown to be complete not by -constant weight alone, but by testing for oxides of nitrogen with -starch paste rendered extremely sensitive with potassium iodide. That -the test should be reliable, Morse and Burton have pointed out that all -the reagents used must be free from oxidizing agents. The presence of -iodate in the iodide is especially to be avoided. This was removed by -boiling the solution with zinc amalgam. Air was removed from all the -solutions by boiling.</p> - -<p>When the starch-potassium-iodide solution had been prepared as -sensitive as possible, a portion of it was treated with a little -<span class="pagenum" id="Page_36">[Pg 36]</span> -hydrochloric acid, to determine if any iodine was liberated. If no -coloration was observed the cadmium oxide was added. It dissolved in -the hydrochloric acid and if any oxides of nitrogen were present they -would have revealed themselves by the liberation of iodine and a blue -coloration of the starch paste.</p> - -<p>In no one of the ten determinations was the slightest coloration -detected.</p> - -<p>An equal volume of nitric acid was added to the pair of crucibles used -as a tare as to those containing the determination, and they were -heated in exactly the same manner and for the same length of time.</p> - -<p>The crucibles containing the cadmium oxide were heated over the -blast-lamp for an hour, weighed against their tare, reheated, again -<span class="pagenum" id="Page_37">[Pg 37]</span> -weighed, and this continued until there was no further change in -weight. Usually from two to four hours heating over the blast-lamp was -sufficient to completely decompose the nitrate. The test for oxides of -nitrogen was then applied.</p> - -<p>I found that practically constant weight could be reached short of -compete decomposition, at a temperature below that necessary to -transform all the nitrate into the oxide. This necessitated the final -test for oxides of nitrogen.</p> - -<h3 id="Weigh_1">The Weighing.</h3> - -<p>The balance used was a No. 8 long-armed one, made by Becker and Sons. -It was supported by iron brackets fastened to one of the foundation -walls of the laboratory. -<span class="pagenum" id="Page_38">[Pg 38]</span></p> - -<p>Here it would be subjected to the least jar and was also well protected -from air currents. All weighings were made between the hours of one and -five in the morning when the surroundings were as quiet as could be -desired. A very slight disturbance was detected by the vibrations on -the surface of a cup of mercury placed conveniently between the pans.</p> - -<p>That the presence of the operator might not produce any change in the -balance during the weighing, he closed the room, placed the light above -and behind his head and took his position in front of the balance at -least an hour before making a weighing. When his presence no longer -affected the balance (which was shown by the zero point remaining -<span class="pagenum" id="Page_39">[Pg 39]</span> -constant in a series of determinations) the weighing was begun. The -method of weighing by vibrations and upon both pans was employed -throughout.</p> - -<p>Each zero point was taken as the mean of three closely agreeing zero -determinations; each one of the three being the mean of seven readings. -The zero of the balance empty was determined just before and after -each weighing to detect any change in its position. Usually none was -observed. The sensibility of the balance was taken at each weighing -with the weights used at that weighing. A displacement of the zero -point about six divisions of the ivory scale was effected by the -addition of one milligram.</p> - -<p>The weights had been especially adjusted and were carefully compared -with each other before using. -<span class="pagenum" id="Page_40">[Pg 40]</span></p> - -<p>Weighing by tares was adopted as preferable to any other method. By -this means all errors resulting from changes in the moisture of the air -were avoided and any errors which might have been introduced by heating -or manipulating the crucibles would be counteracted by treating the -tare in exactly the same manner.</p> - -<h3 id="Tare">Taring The Crucibles.</h3> - -<p>A pair of crucibles (<a href="#FIG_3">1 and 2 in the figure</a>) was selected -and treated as described. Another pair about the same size but a little lighter -was prepared in exactly the same way. Each pair was placed in the nickel -crucible and heated by means of the blast-lamp for half an hour. -<span class="pagenum" id="Page_41">[Pg 41]</span></p> - -<p>After cooling in desiccators, both pairs of crucibles where placed -in the closed balance until no longer affected by the moisture of the -air, which was also dried by calcium chloride. The tare was brought to -within one tenth of a milligram of the weight of the crucibles against -which it was being tared, by adding fragments of porcelain obtained -from another crucible of the same composition. The difference in weight -between the tare and its mate was then accurately ascertained.</p> - -<p>Each pair of crucibles was again placed in the nickel crucible and -blasted for half an hour. They were then reweighed, to determine if the -difference in weight previously found had remained constant. In no case -was any change detected, yet this precaution was always taken. -<span class="pagenum" id="Page_42">[Pg 42]</span></p> - -<h3 id="Results_1">The Results.</h3> - -<p class="space-below2">The following table contains the results of ten -successive determinations.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary="Results" cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdc" colspan="3"> </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - </tr><tr> - <th class="tdc bb"> </th> - <th class="tdc bb"> Wt. of Cd. </th> - <th class="tdc bb"> Wt. of CdO. </th> - <th class="tdc bb">(O = 16)</th> - <th class="tdc bb">(O = 15.96)</th> - </tr> - </thead> - <tbody><tr> - <td class="tdr">I </td> - <td class="tdc">1.77891</td> - <td class="tdc">2.03288</td> - <td class="tdc">112.070</td> - <td class="tdc">111.790</td> - </tr><tr> - <td class="tdr">II </td> - <td class="tdc">1.82492</td> - <td class="tdc">2.08544</td> - <td class="tdc">112.078</td> - <td class="tdc">111.798</td> - </tr><tr> - <td class="tdr">III </td> - <td class="tdc">1.74688</td> - <td class="tdc">1.99626</td> - <td class="tdc">112.078</td> - <td class="tdc">111.798</td> - </tr><tr> - <td class="tdr">IV </td> - <td class="tdc">1.57000</td> - <td class="tdc">1.79418</td> - <td class="tdc">112.053</td> - <td class="tdc">111.773</td> - </tr><tr> - <td class="tdr">V </td> - <td class="tdc">1.98481</td> - <td class="tdc">2.26820</td> - <td class="tdc">112.061</td> - <td class="tdc">111.781</td> - </tr><tr> - <td class="tdr">VI </td> - <td class="tdc">2.27297</td> - <td class="tdc">2.59751</td> - <td class="tdc">112.059</td> - <td class="tdc">111.779</td> - </tr><tr> - <td class="tdr">VII </td> - <td class="tdc">1.75695</td> - <td class="tdc">2.00775</td> - <td class="tdc">112.086</td> - <td class="tdc">111.806</td> - </tr><tr> - <td class="tdr">VIII </td> - <td class="tdc">1.70028</td> - <td class="tdc">1.94305</td> - <td class="tdc">112.059</td> - <td class="tdc">111.779</td> - </tr><tr> - <td class="tdr">IX </td> - <td class="tdc">1.92237</td> - <td class="tdc">2.19679</td> - <td class="tdc">112.083</td> - <td class="tdc">111.803</td> - </tr><tr> - <td class="tdr bb">X </td> - <td class="tdc bb">1.92081</td> - <td class="tdc bb">2.19502</td> - <td class="tdc bb">112.078</td> - <td class="tdc bb">111.798</td> - </tr><tr> - <td class="tdr" colspan="3">Mean, </td> - <td class="tdc">112.0705.</td> - <td class="tdc">111.7905.</td> - </tr><tr> - <td class="tdr" colspan="3">Maximum, </td> - <td class="tdc">112.086.</td> - <td class="tdc">111.806.</td> - </tr><tr> - <td class="tdr" colspan="3">Minimum, </td> - <td class="tdc">112.053.</td> - <td class="tdc">111.773.</td> - </tr><tr> - <td class="tdr" colspan="3">Difference, </td> - <td class="tdc">   .033.</td> - <td class="tdc">   .033.</td> - </tr> - </tbody> -</table> - -<p class="space-above2"><span class="pagenum" id="Page_43">[Pg 43]</span> -Calculating the atomic weight of cadmium from the total amount of metal -used and oxide found, we have:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary="Results" cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdc">At. Wt. of Cd.</th> - <th class="tdc">At. Wt. of Cd.</th> - </tr><tr> - <th class="tdc bb">(O = 16)</th> - <th class="tdc bb">(O = 15.96)</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc">112.0706.</td> - <td class="tdc">111.7904.</td> - </tr> - </tbody> -</table> - -<p>These results agree more closely with those of von Hauer and Lenssen -than with those of any other experimenter. The following table gives -a comparison of the work of these investigators with that herein described: -<span class="pagenum" id="Page_44">[Pg 44]</span></p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdc"> </th> - <th class="tdc">von Hauer.</th> - <th class="tdc">Lenssen.</th> - <th class="tdc">Work here described.</th> - </tr><tr> - <th class="tdc"> </th> - <th class="tdc">9 determinations.</th> - <th class="tdc">3 determinations.</th> - <th class="tdc">10 determinations.</th> - </tr><tr> - <th class="tdc bb"> </th> - <th class="tdc bb">(O = 16)</th> - <th class="tdc bb">(O = 16)</th> - <th class="tdc bb">(O = 16)</th> - </tr> - </thead> - <tbody><tr> - <td class="tdl">Mean </td> - <td class="tdc">111.940</td> - <td class="tdc">112.067</td> - <td class="tdc">112.0705</td> - </tr><tr> - <td class="tdl">Max. </td> - <td class="tdc">112.121</td> - <td class="tdc">112.304</td> - <td class="tdc">112.086</td> - </tr><tr> - <td class="tdl">Min. </td> - <td class="tdc">111.796</td> - <td class="tdc">111.911</td> - <td class="tdc">112.053</td> - </tr><tr> - <td class="tdl">Diff. </td> - <td class="tdc">  .325</td> - <td class="tdc">  .393</td> - <td class="tdc">  .033</td> - </tr> - </tbody> -</table> - -<p>A difference of three or four tenths of a unit between the different -results of a series leaves considerable doubt as to the accuracy of the -method employed and to the value obtained.</p> - -<p>The figure selected by Ostwald,<a id="FNanchor_5" href="#Footnote_5" class="fnanchor">[5]</a> -as most probable for the atomic weight of cadmium is 112.08. This is -the mean of the results on von Hauer and Huntington. My own work -leads me to believe that this number is very close to the true value -when oxygen is taken as 16.</p> - -<h3 id="Objections_1">Objections to the method.</h3> - -<p>Marignac<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">[6]</a> -offered the objection to this method for determining the -atomic weight of zinc that the zinc oxide dissociated when heated in -platinum over the blast-lamp. The same objection might be urged against -this method for determining the atomic weight of cadmium, had it not -been shown that the objection does not hold for zinc<a id="FNanchor_7" href="#Footnote_7" class="fnanchor">[7]</a>. -What took place was a reduction of the zinc oxide by the highly heated -hydrogen which passed through the hot platinum. -<span class="pagenum" id="Page_46">[Pg 46]</span></p> - -<p>It was shown that zinc oxide can be heated in a platinum vessel in a -muffle furnace, to the melting point of steel, without undergoing any -dissociation, or in any wise losing in weight. This source of error was -avoided by using porcelain vessels, which were not brought into contact -with the free flame.</p> - -<p>The statement of Marignac that the oxide of zinc derived from the -nitrate retains oxides of nitrogen even when heated to the temperature -at which it begins to undergo dissociation, was shown by the same -authors to be without foundation. The basis of this objection is -doubtless to be found in the imperfect method of testing for such oxides. -<span class="pagenum" id="Page_47">[Pg 47]</span></p> - -<p>It might be urged as an objection to this method that the difference -in weight between the metal and oxide is not very great, therefore any -error in weighing would be multiplied in the result. At first sight -this objection may appear valid, but since the substances weighed were -so well adapted to that purpose and the weighings could be made with -such a high degree of accuracy no appreciable error could have resulted -from this source.</p> - -<p>A crucible with its contents was repeatedly weighed against its tare -and weights to ascertain the difference between successive weighings -under the conditions employed. A number of weighings agreed to .00002 -gr. and in some instances to half this amount. -<span class="pagenum" id="Page_48">[Pg 48]</span></p> - -<h3 id="Advantages_1">Advantages of the Method.</h3> - -<div class="blockquot"> -<p class="neg-indent">1 The great advantage of the method is its -extreme simplicity. From the beginning of an experiment until the end -the contents of the crucible are not brought into contact with any -foreign substance. By this means small errors resulting from incomplete -precipitation, and filtration and all other errors incident to ordinary -processes of analysis were avoided.</p> - -<p class="neg-indent">2 The nature of the metal and its oxide rendered -them well adapted to weighing. The specific gravity of the metal -and oxide approached so closely to that of the weights, that it was -unnecessary to reduce the weighings to a vacuum standard. -<span class="pagenum" id="Page_49">[Pg 49]</span></p> - -<p class="neg-indent">3 The advantages derived from weighing by tares -have been pointed out.</p> - -<p class="neg-indent">4 The closely agreeing results speak strongly in -favor of the accuracy of the method.</p> -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_50">[Pg 50]</span></p> -<h2 class="nobreak" id="Oxalate">The Oxalate Method.</h2> -</div> - -<p>The method consists in taking a weighed amount of cadmium oxalate, -decomposing it by heat, when a mixture of oxide and metal are said -to be formed, dissolving this mixture in nitric acid, converting the -nitrate into oxide and weighing the oxide.</p> - -<p>Lenssen<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">[8]</a> -obtained results by this method which agree very closely with those -recorded in the earlier part of this dissertation.</p> - -<p>Working with the same method, Partridge<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">[9]</a> -arrived at a value about one fourth of a unit lower than that of Lenssen. -<span class="pagenum" id="Page_51">[Pg 51]</span></p> - -<p>It appeared desirable that this method should be repeated with the -greatest care to ascertain what result it would give under the most -favorable conditions.</p> - -<p>Having a supply of pure cadmium it was necessary to prepare pure -oxalic acid.</p> - -<h3 id="Oxalic">Preparation of Pure Oxalic Acid.</h3> - -<p>The commercial acid was crystallized three times from cold water to -separate it from acid oxalates. It was then boiled for two days with -a 15 per cent solution of hydrochloric acid, to remove any mineral -matter present. The acid which crystallized from the hydrochloric acid -solution was recrystallized twice from hot, redistilled alcohol and -<span class="pagenum" id="Page_52">[Pg 52]</span> -twice from pure ether. It was finally boiled with water to decompose -any ethyl oxalate and twice crystallized from pure water. The acid was -dried in the air at ordinary temperatures. This acid left no residue on -ignition.</p> - -<h3 id="Prep_Oxalate">Preparation of Cadmium Oxalate.</h3> - -<p>A piece of cadmium was dissolved in pure nitric acid. On carefully -evaporating the solution cadmium nitrate was obtained. Twenty-five -grams of the nitrate were dissolved in 750 c.c. of redistilled water. -Somewhat less than an equivalent of the oxalic acid was dissolved in an -equal volume of water, and slowly added to the solution of the nitrate -with constant shaking. A little less than an equivalent of oxalic acid -<span class="pagenum" id="Page_53">[Pg 53]</span> -was used to avoid any tendency to form acid oxalates. Cadmium oxalate -was precipitated on standing a few minutes as a white crystalline -compound, well adapted to washing. The oxalate was filtered off and -washed until the wash water was free from all traces of nitric acid. It -was then washed ten times with water which had been twice redistilled -and dried in an air-bath for twenty hours at 150°C.</p> - -<p>The arrangement of the crucibles which were weighed was in all respects -like that in the preceding method.</p> - -<h3 id="Mode_2">Mode of Procedure.</h3> - -<p>The crucibles were heated, tared, and weighed exactly as in the -<span class="pagenum" id="Page_54">[Pg 54]</span> -preceding method. The oxalate was weighed in ground-stoppered weighing -tubes from which it was transferred to the inner of the two porcelain -crucibles. The pair of crucibles, (<a href="#FIG_3">1 and 2 fig. 3</a>) was placed -in a third porcelain crucible and the whole system introduced into an -upright air-bath. The outer crucible was supported on a porcelain -triangle about an inch from the bottom of the bath and was not allowed -to touch its walls at any point. The top of the bath was covered with a -sheet of iron over which was placed an asbestos board. The exterior was -also covered with a lining of asbestos. A thermometer was introduced -well into the bath. The temperature was allowed to rise slowly until -the oxalate began to show a brown color around the edge. From this stage -<span class="pagenum" id="Page_55">[Pg 55]</span> -the temperature was kept as low as possible in order to effect the -decomposition. When the oxalate was decomposed the bath was allowed to -cool and the contents of the crucible completely dissolved in nitric -acid. The nitrate was evaporated to dryness and decomposed as in the -method first described. The end of the decomposition was determined in -the same manner and the oxide, free from all impurities, weighed.</p> - -<h3 id="Weigh_2">The Drying and Weighing of the Oxalate.</h3> - -<p>It was necessary to dry the oxalate before weighing from fifteen to -twenty hours at 150°C. in addition to the twenty hours drying of the -whole preparation. At this temperature the last traces of moisture were -removed by prolonged heating. -<span class="pagenum" id="Page_56">[Pg 56]</span></p> - -<p>The weighing of the oxalate was made in the weighing glasses in which -it was dried. Two of these glasses had been previously tared against -each other, using the lighter as the tare and adding fragments of -glass to it until the difference in weight was a small fraction of -a milligram. The oxalate having been dried to constant weight, was -weighed. It was then poured as carefully and completely as possible -from the weighing glass into the crucible and the glass again weighed -against its tare. The difference in the two weights gave the amount of -oxalate. The glass and its tare were dried and reweighed to determine -<span class="pagenum" id="Page_57">[Pg 57]</span> -if the few milligrams of oxalate adhering to the walls of the glass -had absorbed any moisture during the transfer of the oxalate. In one -experiment a slight difference was detected when a second drying and -weighing were made.</p> - -<p>The weight of the cadmium oxalate as obtained from the balance was -corrected for the difference in specific gravity between the cadmium -oxalate and the weights. -<span class="pagenum" id="Page_58">[Pg 58]</span></p> - -<h3 id="Results_2"><big>The Results.</big></h3> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdc" colspan="3"> </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - </tr><tr> - <th class="tdc" colspan="3"> </th> - <th class="tdc">(O=16)</th> - <th class="tdc">(O=16)</th> - <th class="tdc">(O=15.96)</th> - <th class="tdc">(O=15.96)</th> - </tr><tr> - <th class="tdc" colspan="3"> </th> - <th class="tdc">(C=12.001)</th> - <th class="tdc">(C=12.003)</th> - <th class="tdc">(C=11.971)</th> - <th class="tdc">(C=11.973)</th> - </tr><tr> - <th class="tdc bb"> </th> - <th class="tdc bb"> CdC₂O₄ </th> - <th class="tdc bb">CdO</th> - <th class="tdc bb"> </th> - <th class="tdc bb"> </th> - <th class="tdc bb"> </th> - <th class="tdc bb"> </th> - </tr> - </thead> - <tbody><tr> - <td class="tdr">I </td> - <td class="tdc">1.53937</td> - <td class="tdc">  .98526</td> - <td class="tdc">112.026</td> - <td class="tdc">112.033</td> - <td class="tdc">111.746</td> - <td class="tdc">111.753</td> - </tr><tr> - <td class="tdr">II </td> - <td class="tdc">1.77483</td> - <td class="tdc"> 1.13582 </td> - <td class="tdc">111.981</td> - <td class="tdc">111.988</td> - <td class="tdc">111.701</td> - <td class="tdc">111.708</td> - </tr><tr> - <td class="tdr">III </td> - <td class="tdc">1.70211</td> - <td class="tdc">1.08949</td> - <td class="tdc">112.049</td> - <td class="tdc">112.056</td> - <td class="tdc">111.769</td> - <td class="tdc">111.776</td> - </tr><tr> - <td class="tdr">IV </td> - <td class="tdc">1.70238</td> - <td class="tdc">1.08967</td> - <td class="tdc">112.051</td> - <td class="tdc">112.058</td> - <td class="tdc">111.771</td> - <td class="tdc">111.778</td> - </tr><tr> - <td class="tdr bb">V </td> - <td class="tdc bb">1.74447</td> - <td class="tdc bb">1.11651</td> - <td class="tdc bb">112.019</td> - <td class="tdc bb">112.026</td> - <td class="tdc bb">111.739</td> - <td class="tdc bb">111.746</td> - </tr><tr> - <td class="tdr" colspan="3">Mean, </td> - <td class="tdc">112.025</td> - <td class="tdc">112.032</td> - <td class="tdc">111.745</td> - <td class="tdc">111.752</td> - </tr><tr> - <td class="tdr" colspan="3">Maximum, </td> - <td class="tdc">112.051</td> - <td class="tdc">112.058</td> - <td class="tdc">111.771</td> - <td class="tdc">111.778</td> - </tr><tr> - <td class="tdr" colspan="3">Minimum, </td> - <td class="tdc">111.981</td> - <td class="tdc">111.988</td> - <td class="tdc">111.701</td> - <td class="tdc">111.708</td> - </tr><tr> - <td class="tdr" colspan="3">Difference, </td> - <td class="tdc">   .070</td> - <td class="tdc">   .070</td> - <td class="tdc">   .070</td> - <td class="tdc">   .070</td> - </tr><tr> - <td class="tdc bt" colspan="7"> </td> - </tr> - </tbody> -</table> - -<p>The values assigned to carbon in the last two columns were found thus—</p> - -<table class="no-wrap fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">When </td> - <td class="tdc">O = 16,</td> - <td class="tdc">C = 12.001,</td> - <td class="tdl_ws1"> when </td> - <td class="tdc">O = 15.96,</td> - <td class="tdc">C = 11.971.</td> - </tr><tr> - <td class="tdc">”</td> - <td class="tdc">O = 16,</td> - <td class="tdc">C = 12.003,</td> - <td class="tdc">”</td> - <td class="tdc">O = 15.96,</td> - <td class="tdc">C = 11.973.</td> - </tr> - </tbody> -</table> - -<p>Calculating the atomic weight directly from all the oxalate used and -oxide found it would give:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" rules="cols" > - <thead><tr> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - <th class="tdc"> At. Wt. Cd. </th> - </tr><tr> - <th class="tdc">(O=16)</th> - <th class="tdc">(O=16)</th> - <th class="tdc">(O=15.96)</th> - <th class="tdc">(O=15.96)</th> - </tr><tr> - <th class="tdc bb">(C=12.001)</th> - <th class="tdc bb">(C=12.003)</th> - <th class="tdc bb">(C=11.971)</th> - <th class="tdc bb">(C=11.973)</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc">112.025.</td> - <td class="tdc">112.032.</td> - <td class="tdc">111.745.</td> - <td class="tdc">111.752.</td> - </tr> - </tbody> -</table> - -<p>There seems about equal evidence for the two values assigned to carbon -when oxygen = 16. The value of cadmium as given by this method is -therefore 112.025 or 112.032. -<span class="pagenum" id="Page_60">[Pg 60]</span></p> - -<p>As will be seen at a glance this figure agrees much more closely with -that of Lenssen than with that of Partridge.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc"> Lenssen </th> - <th class="tdc"> Partridge </th> - <th class="tdc"> My work </th> - - </tr> - </thead> - <tbody><tr> - <td class="tdc">112.043.</td> - <td class="tdc">111.816.</td> - <td class="tdc">112.025 or</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc"> </td> - <td class="tdl">112.032.</td> - </tr> - </tbody> -</table> - -<p>It also agrees fairly well with the figure 112.0706 which I obtained by -the first method described.</p> - -<h3 id="Advantages_2">Advantages of the Method.</h3> - -<p>The method possesses no advantage whatever over the one which involves -starting with the element itself. The oxalate can however be obtained -pure having pure metal. The salt is of definite composition when -perfectly dry.</p> - -<p>The method as carried out avoided the -contact of any foreign material with -the salt after it was weighed.</p> - -<h3 id="Disadvantages">Disadvantages of the Method.</h3> - -<div class="blockquot"> -<p class="neg-indent">1 The avidity with which the dried oxalate -takes up moisture from the air is an objection to its use for the -determination of atomic weights. Even with the greatest care there is a -slight element of uncertainty introduced from this source.</p> - -<p class="neg-indent">2 The oxalate is stated to decompose into a -mixture of the oxide and metal. The temperature required for this -<span class="pagenum" id="Page_62">[Pg 62]</span> -decomposition is somewhat higher than the melting point of cadmium. The -metal heated above its melting point possesses a vapor-tension and loss -in weight must result, whatever precaution is taken in heating. This is -the probable explanation why the results obtained by this method are -lower than those of the preceding.</p> -</div> - -<p>A comparison of the two methods leads me to attach much more importance -to the results of that one which establishes the relation between -cadmium and cadmium oxide directly and I therefore regard the atomic -weight of cadmium as very closely expressed by the figure 112.07 when -oxygen = 16.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_63">[Pg 63]</span></p> -<h2 class="nobreak" id="Sub-compounds">Preparation of Certain<br /> Sub-compounds of Cadmium.</h2> -</div> - -<p><span class="pagenum" id="Page_64">[Pg 64]</span></p> -<h3 id="Historical_2">Historical.</h3> - -<p>Cadmium acts so generally as a bivalent element that it is usually -regarded as entering into combination only where it can play this rôle. -The only compound described, in which it has apparently a lower valence -than two, was prepared by Marchand<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">[10]</a>. -It was obtained by heating cadmium oxalate to the melting point of -lead when a green powder remained behind which resembled chromium -oxide. When heated on the air it appeared to be decomposed into metal -and oxide. When treated with mercury the compound was not altered. An -analysis showed it to have the composition represented by the formula Cd₂O. -<span class="pagenum" id="Page_65">[Pg 65]</span></p> - -<p>A. Vogel<a id="FNanchor_11" href="#Footnote_11" class="fnanchor">[11]</a> -has shown that the green powder described by Marchand consists of a -mixture of the metal and oxide. When this mixture is treated with -dilute acetic acid the metal remains behind as microscopic glistening -globules. The lower the temperature at which the oxalate is decomposed -the more oxide and the less metal were found in the product.</p> - -<p>There was then no compound known in which cadmium acted as if its -valence was less than two when this work was undertaken.</p> - -<p>That it may act with a greater valence was shown by R. Haafs<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">[12]</a>. -He found that when zinc hydroxide was treated with hydrogen dioxide -<span class="pagenum" id="Page_66">[Pg 66]</span> -certain compounds of zinc and oxygen were formed containing more oxygen -than the normal oxide ZnO. The close resemblance between zinc and -cadmium led him to try the same reaction with cadmium. Hydrogen dioxide -was accordingly allowed to act on cadmium hydroxide and the resulting -product analyzed. There were formed Cd₅O₈, Cd₃O₅ and Cd₄O₇. In no case -was the compound CdO₂ obtained. These compounds are described as fairly -stable even at a hundred degrees.</p> - -<h3 id="Prep_Chloride">The Preparation of Cd₄Cl₇.</h3> - -<p>When anhydrous cadmium chloride is heated with metallic cadmium in a -vacuum, or in an atmosphere of nitrogen, to the fusing point of the -<span class="pagenum" id="Page_67">[Pg 67]</span> -chloride, the molten chloride quickly assumes a garnet red color. -In order to investigate this phenomenon a quantity of the chloride -was prepared by dissolving the redistilled metal in an excess of -hydrochloric acid, evaporating the chloride to dryness on a water -bath, and finally removing the water of crystallization by heating in -a current of dry hydrochloric acid gas. The heating was effected by -placing the chloride in a long platinum boat, which was shoved into a -large glass tube, through which was passed a current of the acid gas. -The tube was heated by means of a combustion furnace and the chloride -kept in the molten condition for two or three hours. By this means -a perfectly white crystalline chloride of the composition CdCl₂ was -obtained, free from water or oxychloride. -<span class="pagenum" id="Page_68">[Pg 68]</span></p> - -<p>The chloride and an excess of metal were placed in a long-necked flask -of hard glass and after the displacement of the air by nitrogen, heated -to the melting point of the chloride. The liquid chloride attained its -maximum depth of color in a few minutes, nevertheless the heating was -continued for five hours. When the temperature was allowed to rise much -above the melting point of the chloride the red substance underwent -decomposition and globules of metal collected upon the walls of the -flask. For this reason no more heat was applied than was just necessary -to keep the contents of the flask in a liquid condition. During the -very gradual cooling of the flask it was shaken gently in order to -<span class="pagenum" id="Page_69">[Pg 69]</span> -facilitate the sinking of any metal, which might be mechanically -retained by the chloride.</p> - -<p>On cooling, the solidified mass possesses a slightly greenish tint -which disappeared when cold, the substance having then a grayish white -color and a cleavage resembling that of talc or brucite. When examined -under the microscope it was found to be perfectly homogeneous and free -from metal. It gave no metallic streak when rubbed between agate surfaces.</p> - -<p>An analysis of the first preparation showed the following composition; -<span class="pagenum" id="Page_70">[Pg 70]</span></p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">chloride</td> <td class="tdc">used</td> - <td class="tdc"> .33541</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .21559</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">chlorine</td> <td class="tdc">”</td> - <td class="tdc"> .11943</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.27 per cent.</td> - <td class="tdc" colspan="3">35.61 per cent.</td> - </tr> - </tbody> -</table> - -<p>These proportions are nearly those of a compound having the -composition Cd₄Cl₇, in which the calculated percentages are:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.34</td> - <td class="tdc" colspan="3">35.66</td> - </tr> - </tbody> -</table> - -<p class="blockquot no-indent"><big>(<b>Foot note</b>)</big>. In the paper in the American -Chemical Journal XII, 488, which records this work the analyses and -percentages were calculated on the basis of the atomic weight of -cadmium = 111.7. Although my work since this date has shown that 112.07 -is the true value, yet I think it preferable to use the old number here -since the changes to be introduced would be very slight and the same -results are thereby kept uniform in the two publications. -<span class="pagenum" id="Page_71">[Pg 71]</span></p> - -<p class="space-above1">In order to determine whether the close -approximation to definite atomic proportions might not be accidental, -the material was reheated with an excess of the metal for twenty hours. -The product was analyzed.</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">chloride</td> <td class="tdc">used</td> - <td class="tdc"> 1.45970</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .93904</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">chlorine</td> <td class="tdc">”</td> - <td class="tdc"> .52329</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.33 per cent.</td> - <td class="tdc" colspan="3">35.85 per cent.</td> - </tr> - </tbody> -</table> - -<p>A second preparation of the substance was made in all respects like the -first. Two analyses were made.</p> - -<h4>First Analysis:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">chloride</td> <td class="tdc">used</td> - <td class="tdc"> .61010</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .39235</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">chlorine</td> <td class="tdc">”</td> - <td class="tdc"> .21725</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.31 per cent.</td> - <td class="tdc" colspan="3">35.61 per cent.</td> - </tr> - </tbody> -</table> - -<h4>Second Analysis:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">chloride</td> <td class="tdc">used</td> - <td class="tdc"> .20616</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .13266</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">chlorine</td> <td class="tdc">”</td> - <td class="tdc"> .07352</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.35 per cent.</td> - <td class="tdc" colspan="3">35.66 per cent.</td> - </tr> - </tbody> -</table> - -<p><span class="pagenum" id="Page_73">[Pg 73]</span> -A third preparation was made like the first and second and analyzed.</p> - -<h4>Analysis:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">chloride</td> <td class="tdc">used</td> - <td class="tdc"> .2832 </td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .18244</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">chlorine</td> <td class="tdc">”</td> - <td class="tdc"> .10123</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Chlorine.</td> - </tr><tr> - <td class="tdc" colspan="3">64.42 per cent.</td> - <td class="tdc" colspan="3">35.74 per cent.</td> - </tr> - </tbody> -</table> - -<p class="space-above1">When the new substance is heated it fuses to a -red liquid and then breaks up into metal and the chloride of cadmium. -Its reactions are in general those of a strong reducing agent. Treated -with nitric acid, oxides of nitrogen are liberated. With dilute -hydrochloric, sulphuric and acetic acids it gives free hydrogen. In -the presence of dilute acids it reduces mercuric to mercurous chloride, -or to metallic mercury.</p> - -<p>Three determinations of the reducing power of the substance were made -with a freshly prepared specimen, by dissolving weighed portions in -hydrochloric acid and measuring the hydrogen liberated.</p> - -<p>The following results were obtained:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc bb" colspan="2"> </th> - <th class="tdc bb"> Hydrogen <br /> found.</th> - <th class="tdc bb"> Hydrogen <br /> calculated<br /> for Cd₄Cl₇.</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc">1ˢᵗ</td> - <td class="tdl"> determination</td> - <td class="tdc">15.67 c.c.</td> - <td class="tdc">15.65 c.c.</td> - </tr><tr> - <td class="tdc">2ⁿᵈ</td> - <td class="tdc">”</td> - <td class="tdc">11.80 c.c.</td> - <td class="tdc">11.82 c.c.</td> - </tr><tr> - <td class="tdc">3ʳᵈ</td> - <td class="tdc">”</td> - <td class="tdc">23.00 c.c.</td> - <td class="tdc">23.03 c.c.</td> - </tr> - </tbody> -</table> - -<p>An examination of the analyses shows beyond question that the substance -formed by the action of metallic cadmium on the molten anhydrous -chloride is of definite composition. The proportion of cadmium to -chlorine could not be changed even when the substance was heated with -the metal for twenty hours, while a very short time was sufficient for -its formation when the metal and chloride were melted together.</p> - -<p>It may be possible that a substance possessing these properties is -not a definite chemical compound but a mixture of cadmous and cadmic -chlorides or a solution of one in the other.</p> - -<p>If it were a solution it is difficult to see why the composition of the -solution should be so constant, since the solubility of a substance -is generally altered by a change in temperature. The different -<span class="pagenum" id="Page_76">[Pg 76]</span> -preparations were not made at exactly the same temperature yet the -composition of the different preparations was the same.</p> - -<p>If the substance was a mixture of the two chlorides, when treated with -water the cadmic chloride would most probably dissolve directly leaving -the cadmous chloride to be acted upon by the water. The decomposition -by water will however be seen not to be as simple as would be expected -under these conditions. -<span class="pagenum" id="Page_77">[Pg 77]</span></p> - -<p>From the above considerations it appears highly probable that the -substance is a definite chemical compound of cadmic and cadmous -chlorides. If cadmic chloride can form a chemical compound with the -chloride of another element there appears to be no reason why it should -not form a compound with another chloride of cadmium, as with cadmous chloride. -<span class="pagenum" id="Page_78">[Pg 78]</span></p> - -<h3 id="Prep_Bromide">The preparation of Cd₄Br₇.</h3> - -<p>The anhydrous bromide of cadmium was prepared by dissolving the -carbonate in an aqueous solution of hydrobromic acid, evaporating -the bromide to dryness on the water bath and heating the residue in -a current of dry hydrobromic acid gas. When the bromide was heated -with an excess of the metal in an atmosphere of nitrogen it conducted -itself in general like the chloride. When the molten bromide and the -metal came in contact the salt quickly became deep red in color. After -heating for some time considerable dissociation was produced by raising -the temperature. This was more apparent in the preparation of the -<span class="pagenum" id="Page_79">[Pg 79]</span> -bromide than with the chloride. On cooling, the mass possessed a -greenish tint which disappeared when cold, the bromide then being -very nearly the same color as the corresponding chloride. Also like -the chloride it appeared to be homogeneous and free from metal. Two -determinations of cadmium and two of bromine were made, using the -product as soon as prepared.</p> - -<h4>First determination of cadmium:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .3736 </td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc">.16658</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">44.59 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above3">Second determination of cadmium:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .35930</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc">.16013</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">44.57 per cent.</td> - <td class="tdc" colspan="3"><span class="pagenum" id="Page_80">[Pg 80]</span></td> - </tr> - </tbody> -</table> - -<h4 class="space-above3">First determination of bromine:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .66640</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">bromine</td> <td class="tdc">found</td> - <td class="tdc">.36953</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Bromine.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">55.45 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above3">Second determination of bromine:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .56035</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">bromine</td> <td class="tdc">found</td> - <td class="tdc">.31085</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Bromine.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">55.47 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p>The percentage of cadmium and bromine found agrees very closely with -that of a compound of the formula Cd₄Br₇. The relation of cadmium to -bromine in this would be:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Bromine.</td> - </tr><tr> - <td class="tdc" colspan="3">44.44 per cent.</td> - <td class="tdc" colspan="3">  55.56 per cent.</td> - </tr> - </tbody> -</table> - -<p>When this compound was heated for a long time with an excess of the -metal its composition was not appreciably changed.</p> - -<p>The compound Cd₄Br₇ is a strong reducing agent: giving with nitric -acid oxides of nitrogen, with dilute hydrochloric, sulphuric or acetic -acid, free hydrogen, and with mercuric chloride, mercurous chloride or -metallic mercury. The action of water on the bromide by means of which -cadmous hydroxide was formed, was not studied as carefully as with the -chloride but appeared to be essentially the same. -<span class="pagenum" id="Page_82">[Pg 82]</span></p> - -<h3 id="Prep_Iodide">The Preparation of Cd₁₂I₂₃.</h3> - -<p>Cadmic iodide was prepared in the same manner as the bromide. It was -dried in a stream of hydriodic acid gas at as low temperature as -possible to lessen the decomposition of the hydriodic acid. When the -anhydrous iodide was heated with an excess of metal in an atmosphere of -nitrogen the red color of the iodide became intensified. Heating was -continued until there was evidence of dissociation, which, under the -same conditions, was less marked than with the chloride and much less -than with the bromide. Owing to the high specific gravity of the iodine -compound some difficulty was experienced in obtaining a preparation -<span class="pagenum" id="Page_83">[Pg 83]</span> -free from metal. This difficulty was finally overcome by keeping -the material just above its melting temperature for a long time and -constantly jarring the flask. During the process of cooling a decidedly -greenish tint was observed which disappeared as the process was -continued. When cold the substance resembled the chloride and bromide. -Two determinations of cadmium were made in the first preparation.</p> - -<h4>First determination:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .55540</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc">.17456</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">31.43 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above3">Second determination:</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .47535</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc">.14980</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">31.51 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p>As these results did not correspond to the composition represented by -the formula Cd₄I₇, which our experience with the chloride and bromide -had led us to expect, we reheated the material for several hours with -an excess of the metal. Two analyses of the product gave:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Iodine.</td> - </tr><tr> - <td class="tdc" colspan="3">31.44 per cent.</td> - <td class="tdc" colspan="3">68.65 per cent.</td> - </tr><tr> - <td class="tdc" colspan="3">31.39</td> - <td class="tdc" colspan="3">68.68</td> - </tr> - </tbody> -</table> - -<p class="no-indent">showing that the iodide had taken -up during the first heating all the metal which it could retain. The -analytical results suggest the formula Cd₁₂I₂₃, in which the calculated -percentages are: -<span class="pagenum" id="Page_85">[Pg 85]</span></p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3">Iodine.</td> - </tr><tr> - <td class="tdc" colspan="3">31.53 per cent.</td> - <td class="tdc" colspan="3">68.47 per cent.</td> - </tr> - </tbody> -</table> - -<p>In its conduct towards dilute hydrochloric and acetic acids and water -the substance behaves like the corresponding chloride and bromide.</p> - -<h3 id="Prep_Oxide">The Preparation of<br /> Cadmous Hydroxide and Oxide.</h3> - -<p>When the substance Cd₄I₇ is treated with water a complicated reaction -takes place. The general character of the reaction appears to be the -same with the chloride, bromide and iodide. The decomposition of the -chloride was studied more thoroughly than that of the other compounds.</p> - -<p>When the finely powdered chloride is treated with water it yields -cadmic chloride which passes into solution, a small quantity of a white -flocculent material which may be cadmic hydroxide but which in no case -could be entirely freed from traces of chlorine, and a highly lustrous -crystalline substance which rapidly lost its crystalline appearance and -<span class="pagenum" id="Page_87">[Pg 87]</span> -passed over into a grayish white amorphous compound, which when freed -from chlorine was found to be cadmous hydroxide, of the formula Cd(OH). -The separate products resulting from the treatment with water were -analyzed.</p> - -<h4>First Analysis:</h4> - -<table class="no-wrap fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl" colspan="3">Amount of Cd₄Cl₇</td> - <td class="tdl">treated with water</td> - <td class="tdc"> 1.45970</td> - <td class="tdc">gr.</td> - </tr><tr> - <td class="tdl" colspan="3">Cadmium found in</td> - <td class="tdl">flocculent precipitate</td> - <td class="tdc">  .02318</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">”</td> <td class="tdl">crystalline substance</td> - <td class="tdc"> .09614</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">”</td> <td class="tdl">solution in water</td> - <td class="tdc"> .81970</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdr" colspan="4">Total cadmium found  </td> - <td class="tdc">  .93902</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdr" colspan="6"> </td> - </tr><tr> - <td class="tdl" colspan="3">Chlorine found in</td> - <td class="tdl">crystalline compound</td> - <td class="tdc">  .00371</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">”</td> <td class="tdl">solution in water</td> - <td class="tdc"> .51671</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdr" colspan="4">Total chlorine found  </td> - <td class="tdc">  .52042</td> <td class="tdc">”</td> - </tr> - </tbody> -</table> - -<p class="space-above2">Approximately seven-eighths of the total -cadmium dissolved as cadmic chloride while the remainder was contained -in the flocculent precipitate and in the gray crystalline compound.</p> - -<h4 class="space-above1">Second Analysis:</h4> - -<table class="no-wrap fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl" colspan="3">Amount of Cd₄Cl₇</td> - <td class="tdl">treated with water</td> - <td class="tdc"> 1.0794</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdl" colspan="3">Cadmium found in</td> - <td class="tdl">flocculent precipitate</td> - <td class="tdc">  .01469</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">”</td> <td class="tdl">solution in water</td> - <td class="tdc"> .60795</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdl" colspan="6"> </td> - </tr><tr> - <td class="tdl" colspan="3">Chlorine found in</td> - <td class="tdl">solution in water</td> - <td class="tdc">  .38491</td> <td class="tdc">”</td> - </tr> - </tbody> -</table> - -<p class="space-above2">The percentage of cadmium in the white -precipitate is less in this analysis than in the former. The cadmium -in solution is again about seven-eighths of the total and the chlorine -present in the same solution shows that the cadmium was all combined -as cadmic chloride.</p> - -<p>All attempts to determine the composition of the gray crystalline -compound failed, owing to the rapidity with which it decomposed with -water. Even with the most rapid work it could not be isolated in the -undecomposed condition.</p> - -<p>Analyses of the partially decomposed crystals gave variable proportions -of metal and halogen but never less than eight equivalents of the -former to one of the latter.</p> - -<p>While the decomposition of Cd₄Cl₇ with water cannot at present be fully -explained, yet it is clear from the analyses that one eighth of the -total cadmium is thrown down as a white precipitate and a crystalline -<span class="pagenum" id="Page_90">[Pg 90]</span> -compound which as will be seen passes over into cadmous hydroxide. One -half of the cadmous chloride is oxidized to cadmic chloride taking the -chlorine from the other half.</p> - -<p>The compound Cd₄Cl₇ was treated directly with absolute alcohol with -the hope of obtaining the crystalline substance in an undecomposed -condition. Although a substance of the same general appearance as that -formed in the presence of water was obtained yet it decomposed so -readily that a satisfactory analysis could not be made.</p> - -<p>Notwithstanding the rapidity with which the decomposition of the -crystalline compound begins, long continued washing was necessary in -<span class="pagenum" id="Page_91">[Pg 91]</span> -order to completely remove the chlorine. The extraction of the last -traces of the halogen is hastened by the use of warm instead of cold -water. The temperature of the water must not exceed 50°C. In water -whose temperature approaches the boiling point the hydroxide is slowly -decomposed with liberation of metal.</p> - -<p>The new hydroxide is a strong reducing agent. It dissolves in dilute -acids; yielding with nitric acid oxides of nitrogen, with hydrochloric -or sulphuric acid free hydrogen. After washing with warm water until -all the chlorine had disappeared, it was dried over phosphorus -pentoxide and analyzed. -<span class="pagenum" id="Page_92">[Pg 92]</span></p> - -<h4>First determination of cadmium.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .0968 </td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .08415</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">86.93 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above2">Second determination of cadmium.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .09806</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .08522</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">86.91 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p>The calculated percentage of cadmium in Cd(OH) is:</p> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Cadmium.</td> - </tr><tr> - <td class="tdc">86.79 per cent.</td> - </tr> - </tbody> -</table> - -<p>The determination of water in cadmous hydroxide was made by placing a -small specimen tube containing the hydroxide in a Kjeldahl flask which -was heated in a bath of concentrated sulphuric acid. During the heating -a slow current of dry nitrogen was passed over the substance.</p> - -<h4>First determination of water.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .08434</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">water</td> <td class="tdc">found</td> - <td class="tdc"> .00609</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Water.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">7.22 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above2">Second determination of water.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .08895</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">water</td> <td class="tdc">found</td> - <td class="tdc"> .00600</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Water.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">6.74 per cent.</td> - <td class="tdc" colspan="3"><span class="pagenum" id="Page_94">[Pg 94]</span></td> - </tr> - </tbody> -</table> - -<h4 class="space-above2">Third determination of water.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .11766</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">water</td> <td class="tdc">found</td> - <td class="tdc"> .00856</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Water.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">7.25 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p>Average amount of water = 7.07 per cent.</p> - -<p class="space-below2">The calculated percentage of water in Cd(OH) is, 6.99.</p> - -<p>At the temperature at which concentrated sulphuric acid gives off -dense white fumes cadmous hydroxide gives off all its water and passes -over into a heavy yellow powder. At 150°C not a trace of water was -liberated. Under the microscope the yellow powder was found to consist -of minute translucent crystals.</p> - -<h4>First determination of cadmium.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .08064</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .07511</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">93.14 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<h4 class="space-above2">Second determination of cadmium.</h4> - -<table class="fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdc">Amount</td> <td class="tdc">of</td> - <td class="tdc">substance</td> <td class="tdc">used</td> - <td class="tdc"> .10846</td> <td class="tdc">gr.</td> - </tr><tr> - <td class="tdc">”</td> <td class="tdc">”</td> - <td class="tdc">cadmium</td> <td class="tdc">found</td> - <td class="tdc"> .10106</td> <td class="tdc">”</td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr><tr> - <td class="tdc" colspan="3">Cadmium.</td> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdc" colspan="3">93.17 per cent.</td> - <td class="tdc" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p class="space-below2">The calculated percentage of metal -in Cd₂O is 93.32 per cent.</p> - -<p>If water of too high temperature is employed in washing the -subhydroxide, the presence of free metal in it can be detected under -<span class="pagenum" id="Page_96">[Pg 96]</span> -the microscope and by rubbing between agate surfaces. If the yellow -suboxide is strongly heated it breaks up into a mixture of oxide and -metal which possesses a distinctly green color. Towards acids the -suboxide conducts itself like the subhydroxide.</p> - -<p>It is a fact of some interest in connection with the periodic -arrangement of the elements, that the tendency toward the formation -of a lower series of compounds which becomes so strongly developed in -mercury begins to exhibit itself in some slight degree in cadmium.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_97">[Pg 97]</span></p> -<h2 class="nobreak" id="Notes">Notes on Crystals of Metallic Cadmium.</h2> -</div> - -<p>The measurements of the cadmium crystals were made by Dr. Williams who -has very kindly furnished me with his results.</p> - -<p>No reliable crystallographic description of the element cadmium seems -thus far to have appeared—a fact due to the difficulty in obtaining -suitable material. The crystals examined, although not capable of -yielding entirely satisfactory results are nevertheless such as to make -them of interest.</p> - -<p>In 1852 G. Rose noted the fact that distilled cadmium collected at the -neck of the retort in drops which solidified as complex polyhedral -aggregates<a id="FNanchor_13" href="#Footnote_13" class="fnanchor">[13]</a> -similar to those formed by zinc<a id="FNanchor_14" href="#Footnote_14" class="fnanchor">[14]</a>. -In 1874 Kammerer<span class="pagenum" id="Page_98">[Pg 98]</span> -encountered the same aggregates which he explained as complicated -isometric combinations<a id="FNanchor_15" href="#Footnote_15" class="fnanchor">[15]</a>. -This opinion was cited in 1881 by Rammelsberg<a id="FNanchor_16" href="#Footnote_16" class="fnanchor">[16]</a>. -In 1884 Brögger and Flink stated that in their opinion -zinc, magnesium and probably cadmium were from analogy with beryllium -which they had studied, hexagonal and holohedral.<a id="FNanchor_17" href="#Footnote_17" class="fnanchor">[17]</a></p> - -<p>This supposition has already been substantiated in the case of the two -former elements<a id="FNanchor_18" href="#Footnote_18" class="fnanchor">[18]</a> -while the present material leads to the same result for the last named.</p> - -<p>The cadmium crystals were produced in the same manner as were those of -zinc and magnesium measured before, viz; by distillation in a vacuum. -The appearance of the tubes thus obtained was closely like that in the -other cases. -<span class="pagenum" id="Page_99">[Pg 99]</span></p> - -<p>The polyhedral aggregates were abundant and reached considerable -dimensions. The crystallizing power of the cadmium however, seems to be -less, so that the only crystals suitable for measurement were extremely -minute. The largest individuals were barrel-shaped, like those of zinc -and resembled little piles of basal plates. Their side planes are not -infrequently uneven and bent, probably as the result of the softness -and great ductility of the metal.</p> - -<p>Only the most minute crystals show pyramidal planes of comparative -perfection. These are well suited for a microscopic examination, but -their small size renders their measurement on a reflecting goniometer a -matter of difficulty. After a careful search two crystals were secured -<span class="pagenum" id="Page_100">[Pg 100]</span> -which, although they had a diameter of only one third of a millimeter, -from their microscopic appearances promised good results. Their planes -however were found to give compound reflections and a somewhat -disappointing variation in corresponding angles. On the best crystal -three zones were measured as follows: (normal angles)</p> - -<table class="no-wrap fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <thead><tr> - <th class="tdc bb br" colspan="2">Zone I</th> - <th class="tdc bb br" colspan="2">Zone II</th> - <th class="tdc bb" colspan="2">Zone III</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc"> </td> <td class="tdc br"> </td> - <td class="tdc"> </td> <td class="tdc br"> </td> - <td class="tdc"> </td> <td class="tdc"> </td> - </tr><tr> - <td class="tdl_ws1">0001 : 01<span class="over">1</span>1 =</td> - <td class="tdl_ws1 br"> 62° 35′</td> - <td class="tdl_ws1">0001 : 10<span class="over">1</span>1</td> - <td class="tdl_ws1 br"> 62° 4′</td> - <td class="tdl_ws1">0001 : 1<span class="over">1</span>01</td> - <td class="tdl_ws1">62° 29′</td> - </tr><tr> - <td class="tdl_ws1">0001 : 01<span class="over">1</span>0 =</td> - <td class="tdl_ws1 br"> 89° 50½′</td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1 br"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl_ws1">0001 : 01<span class="over">1</span><span class="over">1</span> =</td> - <td class="tdl_ws1 br">118° 57′</td> - <td class="tdl_ws1">0001 : 10<span class="over">1</span><span class="over">1</span> =</td> - <td class="tdl_ws1 br">118° 28′</td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1"> </td> - </tr> - </tbody> -</table> - -<p>The second crystal was much less satisfactory, since values for the -angle between the base and pyramid (0001): (01<span class="over">1</span>1) -were obtained which varied all the way from 61° 2′ to 63° 43′. These -measurements must therefore be regarded as of little or no value. If we -average the readings for this angle on the first crystal we obtain 62° 23′, -from which</p> - -<p class="f150">a : <span class="u">c</span> = 1 : 1.6544</p> -<p>A comparison of the axial ratios of the four rhombohedral and four -holohedral hexagonal elements gives the following:</p> - -<table class="no-wrap fontsize_110" border="0" cellspacing="0" summary=" " cellpadding="2" > - <tbody><tr> - <td class="tdl" rowspan="4">Rhombohedral.</td> - <td class="tdc" rowspan="4"><img src="images/cbl-4.jpg" alt="" width="23" height="82" /></td> - <td class="tdl_ws1">Bismuth</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.3035</td> - <td class="tdl_ws1">(G. Rose, 1849).</td> - </tr><tr> - <td class="tdl_ws1">Antimony</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.3235</td> - <td class="tdl_ws1">(Laspeyres, 1875).</td> - </tr><tr> - <td class="tdl_ws1">Tellurium</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.3298</td> - <td class="tdl_ws1">(G. Rose, 1849).</td> - </tr><tr> - <td class="tdl_ws1">Arsenic</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.4025</td> - <td class="tdl_ws1">(Zepharovich, 1875).</td> - </tr><tr> - <td class="tdc" colspan="5"> </td> - </tr><tr> - <td class="tdl" rowspan="4">Holohedral.</td> - <td class="tdc" rowspan="4"><img src="images/cbl-4.jpg" alt="" width="23" height="82" /></td> - <td class="tdl_ws1">Zinc</td> - <td class="tdc">   <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.356425</td> - <td class="tdl_ws1">(Williams and Burton, 1889).</td> - </tr><tr> - <td class="tdl_ws1">Beryllium</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.5802</td> - <td class="tdl_ws1">(Brögger, 1884).</td> - </tr><tr> - <td class="tdl_ws1">Magnesium</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.6202</td> - <td class="tdl_ws1">(Williams, 1890).</td> - </tr><tr> - <td class="tdl_ws1">Cadmium</td> - <td class="tdc"> <span class="u">a</span> : ̲<span class="u">c</span> = 1 : 1.6554</td> - <td class="tdl_ws1">(Williams, 1891).</td> - </tr> - </tbody> -</table> - -<p><span class="pagenum" id="Page_102">[Pg 102]</span> -Zinc appears from its axial ratio to belong rather to the rhombohedral -group and this is the only one of the last four elements upon which the -faintest indication of any divergence from a holohedral development -of all of its forms has been observed. On crystals of this substance -there is an occasional rhombohedral alternative of the faces of -certain of the pyramids, although the crystals otherwise appear to be -holohedral.<a id="FNanchor_19" href="#Footnote_19" class="fnanchor">[19]</a></p> - -<p>The crystals of cadmium like those of magnesium show only the -three forms OP (0001), P (10<span class="over">1</span>1)₂, and -<big>∞</big>P (10<span class="over">1</span>0). Brögger and Flink -observed on beryllium the additional forms -<big>∞</big>P₂ (2<span class="over">1</span><span class="over">1</span>0) -and ½P (20<span class="over">2</span>1); while upon zinc a large number -of forms in the zone of the unit pyramid occur.</p> - -<p><span class="pagenum" id="Page_103">[Pg 103]</span> -Not infrequently the cadmium crystals show a tendency toward a -hemimorphic development. This is plainly seen when a large number -of them are examined together under the microscope. The little -barrel-shaped crystals are mostly attached by their sides and yet one -of their ends is often broader than the other. Sometimes they taper -nearly to a point, quite like greenockite crystals.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="Cohesion">The Cohesion Phenomena of Cadmium.</h2> -</div> - -<p>The cohesion phenomena of cadmium are similar to those of zinc -but are still more striking. When a crystal is sharply focused under -the microscope and then gently pressed on the side with the point of a -<span class="pagenum" id="Page_104">[Pg 104]</span> -needle an unbroken pyramidal face is seen to suddenly become striated -parallel to the basal plane, as though a gliding in the basal section -took place. Some of these crystals were kindly examined by Prof. Otto -Mügge of Münster, Germany, who has added so much to our knowledge -of the cohesion phenomena in crystals. He has written in regard to -his observations as follows; “The cadmium crystals as far as their -gliding phenomena are concerned behave quite like zinc. If a crystal -is carefully loosened and then squeezed with a pair of pincers it is -easy to see that the smooth surface where it was attached to the glass -became striated parallel to OP (0001) and that at the same time two -other sets of striations are produced which meet at an angle of about -<span class="pagenum" id="Page_105">[Pg 105]</span> -85° and intersect the trace of the basal plane at about 47½°. The plane -of attachment was selected for observation because it was smoother than -the pyramidal faces. In the above case this plane has the position of -a steep pyramid inclined to the base at an angle of about 100°. The -oblique sets of striations appear to represent gliding planes parallel -to the unit pyramid faces (2P (10ī2) of Rose) as in the case with zinc. -Whether the horizontal striations were due to gliding parallel to the -base I could not certainly decide. Many of the crystals appear when -pinched to be completely overturned, in which cases ordinary bending -accompanies gliding as in the case of gold set. This is shown by the -fact that both faces and striations become rounded.”</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_106">[Pg 106]</span></p> -<h2 class="nobreak" id="Biographical">Biographical Sketch.</h2> -</div> - -<p>Harry Clary Jones was born near New London, Frederick County, Maryland, -Nov. 11ᵗʰ 1865.</p> - -<p class="space-below2">After attending several schools in that state -he entered the Johns Hopkins University in the autumn of 1885 as a -special student of chemistry and physics. He matriculated in 1887 -and received the degree of Bachelor of Arts in 1889, having held an -ordinary and an honorary scholarship. For the last three years he -has continued his studies in the University following chemistry as a -principal subject and mineralogy and geology as subordinates. During -this time he has been appointed twice to a university scholarship, -was lecture assistant to professor Remsen,90-91, and Fellow in chemistry,91-92.</p> - -<div class="footnotes"> -<p class="f150 u space-below1"><b>Footnotes:</b></p> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_1" href="#FNanchor_1" class="label">[1]</a> -Amer. Chem. Journ. 13, 34. 1891.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_2" href="#FNanchor_2" class="label">[2]</a> -Amer. Chem. Journ. X, 311.</p> -</div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_3" href="#FNanchor_3" class="label">[3]</a> -ib. XII, 219.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_4" href="#FNanchor_4" class="label">[4]</a> -Amer. Journ. Science XL, 379.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_5" href="#FNanchor_5" class="label">[5]</a> -Lehrb. d. Allg. Chem. I, 60.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_6" href="#FNanchor_6" class="label">[6]</a> -Archives des Sciences Phys. et Nat. (3) 10, 193.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_7" href="#FNanchor_7" class="label">[7]</a> -Amer. Chem. Journ. X, 148.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_8" href="#FNanchor_8" class="label">[8]</a> -Journ. f. prakt. Chem. 79, 281.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_9" href="#FNanchor_9" class="label">[9]</a> -Amer. Journ. Science XL, 377.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_10" href="#FNanchor_10" class="label">[10]</a> -Pogg. Ann. XXXVIII, 143.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_11" href="#FNanchor_11" class="label">[11]</a> -Jahrb. 1855, 390.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_12" href="#FNanchor_12" class="label">[12]</a> -Ber. 1884, 2249.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_13" href="#FNanchor_13" class="label">[13]</a> -Pogg. Ann. 85, 293.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_14" href="#FNanchor_14" class="label">[14]</a> -Amer. Chem. Journ. 11, 219.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_15" href="#FNanchor_15" class="label">[15]</a> -Ber. d. deutch. Chem. Gesell. 1874, 1724.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_16" href="#FNanchor_16" class="label">[16]</a> -Handb. d. krystallographisch physicalischen Chemie. I, 184.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_17" href="#FNanchor_17" class="label">[17]</a> -Zeits & Kryst. 9, 236.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_18" href="#FNanchor_18" class="label">[18]</a> -Amer. Chem. Journ. 11, 225 and Ibid. 12, 225.</p></div> - -<div class="footnote"><p class="no-indent"> -<a id="Footnote_19" href="#FNanchor_19" class="label">[19]</a> -Amer. Chem. Journ. 11, 224. pl. 2 fig. 8.</p></div> -</div> - -<div class="transnote bbox space-above2"> -<p class="f120 space-above1">Transcriber’s Notes:</p> -<hr class="r5" /> -<p class="indent">The cover image was created by the transcriber, and is in the public domain.</p> -<p class="indent">The illustrations have been moved so that they do not break up - paragraphs and so that they are near to the text they illustrate.</p> -<p class="indent">Typographical and punctuation errors have been silently corrected.</p> -</div> -<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS SUB-COMPOUNDS ***</div> -<div style='text-align:left'> - -<div style='display:block; margin:1em 0'> -Updated editions will replace the previous one—the old editions will -be renamed. -</div> - -<div style='display:block; margin:1em 0'> -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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